theoraenc: Remove unneeded check

running timestamps are guaranteed to be positive and valid since the
GstVideoEncoder base class will clip incoming buffers

CID #1139797

ext/theora/gsttheoraenc.c

@@ -886,8 +886,6 @@ theora_enc_handle_frame (GstVideoEncoder * benc, GstVideoCodecFrame * frame)
   running_time =
       gst_segment_to_running_time (&GST_VIDEO_ENCODER_INPUT_SEGMENT (enc),
       GST_FORMAT_TIME, timestamp);
-  g_return_val_if_fail (running_time >= 0 || timestamp == GST_CLOCK_TIME_NONE,
-      GST_FLOW_ERROR);
 
   GST_OBJECT_LOCK (enc);
   if (enc->bitrate_changed) {