togglerecord: Also check for flushing at the top of the chain function

It would return further down anyway but there's no point in doing
useless work if it can be avoided.

utils/togglerecord/src/togglerecord/imp.rs

@@ -1061,6 +1061,9 @@ impl ToggleRecord {
             if state.eos {
                 return Err(gst::FlowError::Eos);
             }
+            if state.flushing {
+                return Err(gst::FlowError::Flushing);
+            }
         }
 
         let handle_result = if stream != self.main_stream {