gtkicontheme: Check a return value
gtkicontheme: Check a return value

We were already looking at the error anyway, but rewriting things
this way lets coverity see the light.

chergert/gtk,alexlarsson/gtk,Adamovskiy/gtk,jadahl/gtk,jigpu/gtk,jigpu/gtk,grubersjoe/adwaita,chergert/gtk,jigpu/gtk,grubersjoe/adwaita,grubersjoe/adwaita,alexlarsson/gtk,grubersjoe/adwaita,chergert/gtk,davidgumberg/gtk,davidgumberg/gtk,Adamovskiy/gtk,chergert/gtk,Adamovskiy/gtk,alexlarsson/gtk,davidgumberg/gtk,alexlarsson/gtk,jigpu/gtk,alexlarsson/gtk,jadahl/gtk,jigpu/gtk,Adamovskiy/gtk,grubersjoe/adwaita,jadahl/gtk,jadahl/gtk,alexlarsson/gtk,jigpu/gtk,chergert/gtk,davidgumberg/gtk,davidgumberg/gtk,jigpu/gtk,jadahl/gtk,alexlarsson/gtk,Adamovskiy/gtk,chergert/gtk,alexlarsson/gtk,grubersjoe/adwaita,Adamovskiy/gtk,grubersjoe/adwaita,grubersjoe/adwaita,jadahl/gtk,jigpu/gtk,davidgumberg/gtk,davidgumberg/gtk,chergert/gtk,Adamovskiy/gtk,Adamovskiy/gtk,jadahl/gtk,davidgumberg/gtk,jadahl/gtk,chergert/gtk