os: return 0 from check_timers if we touched any of them

Fixes a regression introduced in 0b2f30834b. If a driver posts input
events during a timer function (wacom and synaptics do this during tap
timeouts), ProcessInputEvents() is not called for these events. There are no
new events on any fds, so the events just sit in the queue waiting for
something else to happen.

Fix this by simply returning 0 from check_timers if we ran at least one of
them or reset them all. This way the callers ospoll_wait will exit and
continue with normal processing.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Keith Packard <keithp@keithp.com>

os/WaitFor.c

@@ -143,7 +143,7 @@ check_timers(void)
 {
     OsTimerPtr timer;
 
-    while ((timer = first_timer()) != NULL) {
+    if ((timer = first_timer()) != NULL) {
         CARD32 now = GetTimeInMillis();
         int timeout = timer->expires - now;
 
@@ -157,6 +157,8 @@ check_timers(void)
             /* time has rewound.  reset the timers. */
             CheckAllTimers();
         }
+
+        return 0;
     }
     return -1;
 }