Add missing tag name in error message

When creating a new issue via REST API with a non-existing tag name,
the error message generated by mci_tag_set_for_issue() did not include
the tag's name.

This was caused by reusing the $t_tag variable to store the return value
of tag_get_by_name(), so the original data is no longer available when
the exception is thrown.

Same problem in IssueAddCommand::validate() if the user attempting to
create the issue does not have the required privileges to create tags,
this time due to usage of an uninitialized variable.

Fixes #25996

api/soap/mc_tag_api.php

@@ -167,15 +167,15 @@ function mci_tag_set_for_issue ( $p_issue_id, array $p_tags, $p_user_id ) {
 				);
 			}
 		} else if( isset( $t_tag['name'] ) ) {
-			$t_tag = tag_get_by_name( $t_tag['name'] );
-			if( $t_tag === false ) {
+			$t_get_tag = tag_get_by_name( $t_tag['name'] );
+			if( $t_get_tag === false ) {
 				throw new ClientException(
-					"Tag {$t_tag['name']} not found.",
+					"Tag '{$t_tag['name']}' not found.",
 					ERROR_TAG_NOT_FOUND
 				);
 			}
 
-			$t_tag_id = $t_tag['id'];
+			$t_tag_id = $t_get_tag['id'];
 		} else {
 			throw new ClientException(
 				'Tag without id or name.',

core/commands/IssueAddCommand.php

@@ -221,7 +221,7 @@ function validate() {
 			foreach( $t_issue['tags'] as $t_tag ) {
 				if( $t_tag['id'] === -1 ) {
 					throw new ClientException(
-						sprintf( "User '%d' can't create tag '%s'.", $this->user_id, $t_new_tag ),
+						sprintf( "User '%d' can't create tag '%s'.", $this->user_id, $t_tag['name'] ),
 						ERROR_TAG_NOT_FOUND );
 					}
 			}