QTextEngine crashes for some characters (ones not common in fonts) in case when fallback font families list consist of more than 255 entries.
Could be reproduced with the following code:
for(int b1 = 10;b1 < 300;b1++)
This causes SIGSEGV in QtextEngine::shapeTextWithHarfbuzz() at line
"si.ascent = qMax(actualFontEngine->ascent(), si.ascent);"
due to actualFontEngine==0.