GitLab: Fix system warning when committing

When checkin.php processes the GitLab webhook, an error occurs:
count(): Argument #1 ($var) must be of type Countable|array, null given

This is caused by checking a non-existent 'parents' property from the
Changeset JSON data.

Since we build an array of parents from the JSON data, reuse that to set
the changeset's parent.

Fixes #346

Author: dregad

Source/Source.php

@@ -36,7 +36,7 @@ class SourcePlugin extends MantisSourceBase {
 	 * <rev>  = changeset revision ID (e.g. SVN rev number, GIT SHA, etc.)
 	 * The match is not case-sensitive.
 	 */
-	const CHANGESET_LINKING_REGEX = '/(?:(?<=^|\s)([cdsvp]?):([^:\s][^:\n\t]*):([^:\s]+):)/i';
+	const CHANGESET_LINKING_REGEX = '/(?:(?<=^|[^\w])([cdsvp]?):([^:\s][^:\n\t]*):([^:\s]+):)/i';
 
 	function register() {
 		$this->name = plugin_lang_get( 'title' );

SourceGitlab/SourceGitlab.php

@@ -347,10 +347,6 @@ public function import_commits( $p_repo, $p_commit_ids, $p_branch='' ) {
 	private function json_commit_changeset( $p_repo, $p_json, $p_branch='' ) {
 		echo "processing $p_json->id ... ";
 		if ( !SourceChangeset::exists( $p_repo->id, $p_json->id ) ) {
-			$t_parents = array();
-			foreach( $p_json->parent_ids as $t_parent ) {
-				$t_parents[] = $t_parent;
-			}
 			# Message will be replaced by title in gitlab version earlier than 7.2
 			$t_message = ( !property_exists( $p_json, 'message' ) )
 				? $p_json->title
@@ -364,9 +360,12 @@ private function json_commit_changeset( $p_repo, $p_json, $p_branch='' ) {
 				$t_message
 			);
 
-			if ( count( $p_json->parents ) > 0 ) {
-				$t_parent = $p_json->parents[0];
-				$t_changeset->parent = $t_parent->id;
+			$t_parents = array();
+			foreach( $p_json->parent_ids as $t_parent ) {
+				$t_parents[] = $t_parent;
+			}
+			if( $t_parents ) {
+				$t_changeset->parent = $t_parents[0];
 			}
 
 			$t_changeset->author_email = $p_json->author_email;