dix: reset the OsBuffers after killing all clients

==21860== 24 bytes in 1 blocks are still reachable in loss record 85 of 397
==21860==    at 0x4C2B3F8: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==21860==    by 0x61ED93: AllocateOutputBuffer (io.c:1037)
==21860==    by 0x61E15A: WriteToClient (io.c:764)
==21860==    by 0x457B30: ProcQueryExtension (extension.c:275)
==21860==    by 0x43596B: Dispatch (dispatch.c:432)
==21860==    by 0x425DAB: main (main.c:295)

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Dave Airlie <airlied@redhat.com>

dix/dispatch.c

@@ -465,6 +465,7 @@ Dispatch(void)
     free(clientReady);
     dispatchException &= ~DE_RESET;
     SmartScheduleLatencyLimited = 0;
+    ResetOsBuffers();
 }
 
 static int VendorRelease = VENDOR_RELEASE;