Fix an unbalanced lua stack operation

ewmh_process_state_atom() does a luaA_object_push() at its beginning, but it
doesn't pop that object again. Fix this by, well, popping the object at the end
of the function again.

Signed-off-by: Uli Schlachter <psychon@znc.in>

ewmh.c

@@ -391,6 +391,8 @@ ewmh_process_state_atom(client_t *c, xcb_atom_t state, int set)
         else if(set == _NET_WM_STATE_TOGGLE)
             client_set_urgent(globalconf.L, -1, !c->urgent);
     }
+
+    lua_pop(globalconf.L, 1);
 }
 
 int