Check return of function

[Kleber Tarcísio]

Hi Free Type Team, how are you?
My name is Kleber and I'm a PhD student. I'm working on a technique to help 
developers to find weaknesses in configurable systems. I would like to know 
what you think about this change:
https://github.com/klebertarcisio/freetype2-1/commit/aab3c841f08c3a67914fbd0167ef4ff174116ccf
Regards
Kleber