dix, mi: stop segfaults when a floating device emits events.

For pointers: don't try to set master->valuator fields if there is no master.
For keyboards: check if device is valid before trying to access the fields in
miPointerGetScreen (btw. this disables DGA events for floating keyboards).

Also stop the hideous number of ErrorFs if we request the paired device for a
floating dev.

dix/devices.c

@@ -2265,11 +2265,8 @@ GetPairedDevice(DeviceIntPtr dev)
         dev = dev->u.master;
 
     if (!dev->spriteInfo->paired)
-    {
-        ErrorF("[dix] No device paired with %d (%s).\n", 
-                dev->id, dev->name);
         return NULL;
-    }
+
     return dev->spriteInfo->paired;
 }
 

dix/getevents.c

@@ -736,8 +736,11 @@ GetPointerEvents(EventList *events, DeviceIntPtr pDev, int type, int buttons,
 
     pDev->valuator->lastx = x;
     pDev->valuator->lasty = y;
+    if (master)
+    {
         master->valuator->lastx = x;
         master->valuator->lasty = y;
+    }
 
     if (!coreOnly)
     {

mi/mipointer.c

@@ -529,7 +529,7 @@ miPointerCurrentScreen ()
 _X_EXPORT ScreenPtr
 miPointerGetScreen(DeviceIntPtr pDev)
 {
-    if (!pDev->isMaster && !pDev->u.master)
+    if (!pDev || (!pDev->isMaster && !pDev->u.master))
         return NULL;
 
     return MIPOINTER(pDev)->pScreen;