Add error param when updating project doc with empty title

Added missing error_parameter() call so that when attempting to update
an existing project document with an empty Title, the error message
indicates which field is required.

Fixes #17407

proj_doc_update.php

@@ -46,6 +46,7 @@
 	access_ensure_project_level( config_get( 'upload_project_file_threshold' ), $t_project_id );
 
 	if ( is_blank( $f_title ) ) {
+		error_parameters( lang_get( 'title' ) );
 		trigger_error( ERROR_EMPTY_FIELD, ERROR );
 	}