segfault displaying emoji in label

This issue was discovered through qutebrowser and initially discussed at https://github.com/qutebrowser/qutebrowser/issues/2306 .

When qt tries to display an emoji in a label, it segfaults. To reproduce, run the `test.py` attachment which simply shows a label with the unicode man in business suit levitating in the text. Also attached is the gdb backtrace of the segfault.