QFontEngineFT crash when using non-scalable fonts

On Linux, when a non-scalable font is used, the application will segfault with a floating point exception.

This may be due to a division by zero in qfontengine_ft.cpp, line 1203 caused by units_by_EM being zero for non-scalable (bitmap) fonts.

To trigger/reproduce this problem, I installed the Noto Color Emoji bitmap font and changed some fontconfig properties to activate and give priority to that font. For example, this meant using a .config/fontconfig/fonts.conf that looked like:

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
 <match target="pattern">
    <test name="prgname">
      <string>hipchat.bin</string>
    </test>
    <edit name="family" mode="prepend_first">
      <string>Noto Color Emoji</string>
    </edit>
  </match>
</fontconfig>