sccparse: Ignore invalid timecode during seek as well

sccparse holds last timecode in order to ignore invalid timecode
and fallback to the previous timecode. That should happen
when sccparse is handling seek event too. Otherwise single invalid
timecode before the target seek position will cause flow error.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1508>

video/closedcaption/src/scc_parse/imp.rs

@@ -378,6 +378,10 @@ impl SccParse {
 
             // Still need to scan lines to find the first buffer
             if state.seeking {
+                // Remember this timecode in order to fallback to this one
+                // if invalid timecode is detected during scanning
+                state.last_timecode = Some(timecode);
+
                 drop(state);
                 return Ok(self.state.lock().unwrap());
             }