xprops: Free counter_list_from_results() return value with g_free()

counter_list_from_results directly passes through the results->prop
pointer which is g_malloc memory, so we should free the buffer it
returns with g_free.

!786

src/x11/xprops.c

@@ -1109,7 +1109,7 @@ free_value (MetaPropValue *value)
     case META_PROP_VALUE_SYNC_COUNTER:
       break;
     case META_PROP_VALUE_SYNC_COUNTER_LIST:
-      free (value->v.xcounter_list.counters);
+      g_free (value->v.xcounter_list.counters);
       break;
     }
 }