libpng: Same fix as previous commit for server platform

(cherry picked from commit ec4be71fade1ee5c6171e323d09197f3bf528499)

platform/server/detect.py

@@ -80,7 +80,7 @@ def configure(env):
         env.ParseConfig('pkg-config freetype2 --cflags --libs')
 
     if (env['builtin_libpng'] == 'no'):
-        env.ParseConfig('pkg-config libpng --cflags --libs')
+        env.ParseConfig('pkg-config libpng16 --cflags --libs')
 
     # Sound and video libraries
     # Keep the order as it triggers chained dependencies (ogg needed by others, etc.)