Exit axis labelling if axes are neither rel nor abs

No actual effect since labels_len is always 0 anyway but let's make the
return more explicit.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

src/evdev.c

@@ -2201,7 +2201,8 @@ static void EvdevInitAxesLabels(EvdevPtr pEvdev, int natoms, Atom *atoms)
     {
         labels     = rel_labels;
         labels_len = ArrayLength(rel_labels);
-    }
+    } else
+        return;
 
     memset(atoms, 0, natoms * sizeof(Atom));