mail/claws-mail: add gdk-pixbuf-extra run-dependency

Fixes errors like:

(claws-mail:51313): GdkPixbuf-WARNING **: 12:43:20.914: Error loading XPM image loader: Image type “xpm” is not supported
stock_pixmap.c:836 Condition pix_d->pixbuf != NULL failed

that prevent icons from being displayed after e129c081e39271eda.

PR: 285900
Reported by: Fabian Keil <fk@fabiankeil.de>
Reviewed by: polarian@polarian.dev
Tested by: Chris Hutchinson <portmaster@bsdforge.com>
Approved by: Chris Hutchinson <portmaster@bsdforge.com> (maintainer)