Fix warning in size request when there is no pixbuf
Fix warning in size request when there is no pixbuf

This patch fix a regression introduced in #beec7ccc.
Without the condition, the width returned is -1, which
produces a warning on every action that involves an
applet.

Also fixed format.

Signed-off-by: Germán Póo-Caamaño <679831b636f7f6776b5d7665ebec4c0074d994a9@gnome.org>
GNOME/gnome-panel,GNOME/gnome-panel