mi: handle DGA subtypes when determining the master device.

The subtype in the DGA event is the core type and all ET_ event types (where
applicable) are identical to the core types. Thus the switch statement below
will work as required and assign the right master device.

Fixes a crasher bug on keyboard devices with valuators. If a device sends a
motion event while grabbed and a DGA client is active (but has not selected
input through DGA), the valuator event is posted through the VCK and
eventually results in a NULL-pointer dereference on dev->valuator.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
(cherry picked from commit 31ab9f8860)

mi/mieq.c

@@ -320,6 +320,7 @@ CopyGetMasterEvent(DeviceIntPtr sdev,
 {
     DeviceIntPtr mdev;
     int len = original->any.length;
+    int type = original->any.type;
 
     CHECKEVENT(original);
 
@@ -327,7 +328,12 @@ CopyGetMasterEvent(DeviceIntPtr sdev,
     if (!sdev || !sdev->u.master)
         return NULL;
 
-    switch(original->any.type)
+#if XFreeXDGA
+    if (type == ET_DGAEvent)
+        type = original->dga_event.subtype;
+#endif
+
+    switch(type)
     {
         case ET_KeyPress:
         case ET_KeyRelease: