out-of-bounds read check should be added to KTX texture reading

The code at [https://code.qt.io/cgit/qt3dstudio/qt3d-
runtime.git/tree/src/runtime/q3dsimageloaders_p.h#n946|https://code.qt.io/cgit/qt3dstudio/qt3d-
runtime.git/tree/src/runtime/q3dsimageloaders_p.h#n946] increments pointers and
reads data without proper checks to ensure the data is still within bounds.

The KTX handler in qtbase appears to do a better job of this:
https://code.qt.io/cgit/qt/qtbase.git/tree/src/gui/util/qktxhandler.cpp#n143

The version in qt3dstudio should be fixed.