[sipmsgops] fix codec_delete_XX() parsing (2)

Issue discovered during OpenSIPS Security Audit 2021,
	by Alfred Farrugia & Sandro Gauci (Enable Security)

GHSA-67w7-g4j8-3wcx
(cherry picked from commit c6ab3bb)

modules/sipmsgops/codecs.c

@@ -366,7 +366,8 @@ int delete_sdp_line( struct sip_msg * msg, char * s, struct sdp_stream_cell *str
 
 	while(*end != '\n' && end < (stream->body.s+stream->body.len) )
 		end++;
-	end++;
+	if ( *end == '\n')
+		end++;
 
 	/* delete the entry */
 	if( del_lump(msg, start - msg->buf, end - start,0) == NULL )