pidgin/pidgin

Fix an issue where we would get a warning about gplugin.pc not found while generating gir files

Testing Done:
built the gir's and made sure the warning was gone.

Reviewed at https://reviews.imfreedom.org/r/151/
libpurple/data/purple-url-handler.desktop.in
libpurple/protocols/null/nullprpl.c
pidgin/data/im.pidgin.Pidgin.desktop.in
sub/libpurple/data/purple-url-handler.desktop.in
sub/libpurple/protocols/null/nullprpl.c
sub/pidgin/data/im.pidgin.Pidgin.desktop.in