basesrc: default return TRUE for latency-events reaching the src

The src is the final stop for this event, and the default result is FALSE
for all sources not implementing event handling, which again will result
in a warning about latency not being able to be configured.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=667299

libs/gst/base/gstbasesrc.c

@@ -1773,6 +1773,9 @@ gst_base_src_default_event (GstBaseSrc * src, GstEvent * event)
       result = TRUE;
       break;
     }
+    case GST_EVENT_LATENCY:
+      result = TRUE;
+      break;
     default:
       result = FALSE;
       break;