pidgin/pidgin

Fix some warnings and other stuff that was missed when porting Jabber to Birb

Testing Done:
Touched all of the files in `libpurple/protocols/jabber`, compiled and verified there were no warnings.

Reviewed at https://reviews.imfreedom.org/r/2932/
i18n = import('i18n')
# use the glib preset which is defined at
# https://github.com/mesonbuild/meson/blob/master/mesonbuild/modules/i18n.py#L93
# at the time of this comment.
i18n.gettext(GETTEXT_PACKAGE, preset : 'glib')
devenv.append('PURPLE_LOCALE_DIR', meson.current_build_dir())