fontforge: fix linking against libpng
This update fixes the following issue with fontforge:
- bnc#867041: Fix linking against libpng. Wrong linking can cause segmenation fault.
-
Submitted by
Petr Gajdos (pgajdos)
Fixed bugs
bnc#867041
fontforge segfaults if both libpng12-0 and libpng15-15 are installed
