Do not send empty events to gpm.  (Keyboards are assumed to have scroll
wheel these days, that makes them part-mouse.  That means typing on
keyboard generates empty mouse events).

From: Dmitry Torokhov <dtor_core@ameritech.net>
Signed-off-by: NPavel Machek <pavel@suse.cz>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>