Ensure enough buttons are advertised to pass the button mapping.

Some buttons are mapped to higher button numbers. For example, BTN_0 is
posted as button 8 if BTN_LEFT is present. On top of that, the
driver-specific button mapping may map the button to something else again.
We need to take these mappings into account when counting the number of
buttons on the device.

Example: A device with BTN_LEFT and BTN_0 and a mapping from 1 -> 7 and 8 ->
2.

BTN_LEFT is mapped to 1. 1 is mapped to 7. num_buttons is 7.
BTN_0 is mapped to 8. 8 is mapped to 2. num_buttons remains 7.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
(cherry picked from commit b358f1eb3a)

src/evdev.c

@@ -1466,8 +1466,14 @@ EvdevProbe(InputInfoPtr pInfo)
     /* count all buttons */
     for (i = BTN_MISC; i < BTN_JOYSTICK; i++)
     {
+        int mapping = 0;
         if (TestBit(i, pEvdev->key_bitmask))
-            num_buttons++;
+        {
+            mapping =
+                pEvdev->btnmap[EvdevUtilButtonEventToButtonNumber(pEvdev, i)];
+            if (mapping > num_buttons)
+                num_buttons = mapping;
+        }
     }
 
     if (num_buttons)