Crash on keyboard input

Commit 1aab68648d3aa38811be38b5bbd3a0704e17ccf8 introduced a regression, which makes Qt unusable (at least for me) because the program crashes/asserts on keyboard input.

ASSERT: "uint(i) < uint(size())" in file src/corelib/tools/qstring.h, line 851

For example in examples/widgets/widgets/lineedits when I press tab after starting the example it exits with an assert.

When I revert the aforementioned commit the assert is not triggered and the program works as expected.