[wasm] QWasmString::toQString() cause assertion failure for emscripten 1.39.4

    I got the latest qt source from git today and built qt-5.14 webassembly with emscripten 1.39.4-fastcomp with the following command:

./configure -opensource -confirm-license -xplatform wasm-emscripten -feature-thread -nomake examples -nomake tests -skip qt3d -skip qtdeclarative -skip qtmultimedia -skip qttools -skip qtxmlpatterns -prefix /usr/local/qt5-wasm-em-1.39.4-fastcomp

The qt wasm module fail to load with the simplest sample program in chrome browser:

qtloader.js:372 Assertion failed: stringToUTF16(str, outPtr, maxBytesToWrite) is missing the third parameter that specifies the length of the output buffer!
qtloader.js:382 Assertion failed: stringToUTF16(str, outPtr, maxBytesToWrite) is missing the third parameter that specifies the length of the output buffer!
qtloader.js:382 exception thrown: RuntimeError: abort(Assertion failed: stringToUTF16(str, outPtr, maxBytesToWrite) is missing the third parameter that specifies the length of the output buffer!) at Error
at jsStackTrace (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:2042:17)
at stackTrace (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:2059:16)
at abort (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:1768:44)
at assert (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:805:5)
at stringToUTF16 (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:1168:3)
at __emval_call (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:6912:23)
at QWasmString::toQString(emscripten::val const&) [__ZN11QWasmString9toQStringERKN10emscripten3valE] (wasm-function[793]:0x24310)
at QWasmIntegration::QWasmIntegration() [__ZN16QWasmIntegrationC2Ev] (wasm-function[581]:0x17079)
at QWasmIntegrationPlugin::create(QString const&, QStringList const&) [__ZN22QWasmIntegrationPlugin6createERK7QStringRK11QStringList] (wasm-function[564]:0x16311)
at QPlatformIntegrationPlugin::create(QString const&, QStringList const&, int&, char**) [__ZN26QPlatformIntegrationPlugin6createERK7QStringRK11QStringListRiPPc] (wasm-function[9612]:0x4167cb),RuntimeError: abort(Assertion failed: stringToUTF16(str, outPtr, maxBytesToWrite) is missing the third parameter that specifies the length of the output buffer!) at Error
at jsStackTrace (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:2042:17)
at stackTrace (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:2059:16)
at abort (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:1768:44)
at assert (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:805:5)
at stringToUTF16 (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:1168:3)
at __emval_call (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:6912:23)
at QWasmString::toQString(emscripten::val const&) [__ZN11QWasmString9toQStringERKN10emscripten3valE] (wasm-function[793]:0x24310)
at QWasmIntegration::QWasmIntegration() [__ZN16QWasmIntegrationC2Ev] (wasm-function[581]:0x17079)
at QWasmIntegrationPlugin::create(QString const&, QStringList const&) [__ZN22QWasmIntegrationPlugin6createERK7QStringRK11QStringList] (wasm-function[564]:0x16311)
at QPlatformIntegrationPlugin::create(QString const&, QStringList const&, int&, char**) [__ZN26QPlatformIntegrationPlugin6createERK7QStringRK11QStringListRiPPc] (wasm-function[9612]:0x4167cb)
at abort (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:1774:9)
at assert (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:805:5)
at stringToUTF16 (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:1168:3)
at __emval_call (eval at completeLoadEmscriptenModule (http://localhost:8080/qtloader.js:443:14), <anonymous>:6912:23)
at __ZN11QWasmString9toQStringERKN10emscripten3valE (wasm-function[793]:0x24310)
at __ZN16QWasmIntegrationC2Ev (wasm-function[581]:0x17079)
at __ZN22QWasmIntegrationPlugin6createERK7QStringRK11QStringList (wasm-function[564]:0x16311)
at __ZN26QPlatformIntegrationPlugin6createERK7QStringRK11QStringListRiPPc (wasm-function[9612]:0x4167cb)
at _Z11qLoadPluginI20QPlatformIntegration26QPlatformIntegrationPluginJRK11QStringListRiRPPcEEPT_PK14QFactoryLoaderRK7QStringDpOT1 (wasm-function[17682]:0x55ab3c)
at _ZN27QPlatformIntegrationFactory6createERK7QStringRK11QStringListRiPPcS2 (wasm-function[17680]:0x55aac7)

This seems to be a regression introduced by a recent commit: 0a4c5b5119ccefc355fe737f03ec330e70c33ec9