usb-hid: Fix 0/0 position for Windows in tablet mode

For unknown reasons, Windows drivers (tested with XP and Win7) ignore
usb-tablet events that move the pointer to 0/0. So always report 0/0 as
1/0.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NAndrzej Zaborowski <andrew.zaborowski@intel.com>

hw/usb-hid.c

@@ -459,6 +459,11 @@ static void usb_pointer_event_combine(USBPointerEvent *e, int xyrel,
     } else {
         e->xdx = x1;
         e->ydy = y1;
+        /* Windows drivers do not like the 0/0 position and ignore such
+         * events. */
+        if (!(x1 | y1)) {
+            x1 = 1;
+        }
     }
     e->dz += z1;
 }