dix: fix GetMaximumEventsNum(), may return a DCCE event too.

Signed-off-by: Peter Hutterer <peter.hutterer@redhat.com>

dix/getevents.c

@@ -486,6 +486,9 @@ GetMaximumEventsNum(void) {
 #endif
         ret *= 2;
 
+    /* One possible DeviceClassesChangedEvent */
+    ret++;
+
     return ret;
 }