Fix querying zero projects

Fix the new api functions, to support the case when a user doesn't have
any accessible project. In this case the filter query can't be built, so
fix returning empty values.

Affected functions were introduced in relation to Issues #20424, #21072.

core/database_api.php

@@ -1314,3 +1314,13 @@ function db_mysql_fix_utf8( $p_string ) {
 		$p_string
 	);
 }
+
+/**
+ * Creates an empty record set, compatible with db_query() result
+ * This object can be used when a query can't be performed, or is not needed,
+ * and still want to return an empty result as a transparent return value.
+ * @return \ADORecordSet_empty
+ */
+function db_empty_result() {
+	return new ADORecordSet_empty();
+}

core/filter_api.php

@@ -1049,6 +1049,10 @@ function filter_unique_query_clauses( array $p_query_clauses ) {
  * @return integer
  */
 function filter_get_bug_count( array $p_query_clauses ) {
+	# If query caluses is an empty array, the query can't be created
+	if( empty( $p_query_clauses ) ) {
+		return 0;
+	}
 	$p_query_clauses = filter_unique_query_clauses( $p_query_clauses );
 	$t_select_string = 'SELECT Count( DISTINCT {bug}.id ) as idcnt ';
 	$t_from_string = ' FROM ' . implode( ', ', $p_query_clauses['from'] );
@@ -1163,6 +1167,13 @@ function filter_get_bug_rows_filter( $p_project_id = null, $p_user_id = null ) {
  * @return IteratorAggregate|boolean adodb result set or false if the query failed.
  */
 function filter_get_bug_rows_result( array $p_query_clauses, $p_count = null, $p_offset = null ) {
+	# if the query can't be formed, there are no results
+	if( empty( $p_query_clauses ) ) {
+		# reset the db_param stack that was initialized by "filter_get_bug_rows_query_clauses()"
+		db_param_pop();
+		return db_empty_result();
+	}
+
 	if( null === $p_count ) {
 		$t_count = -1;
 	} else {

core/history_api.php

@@ -196,6 +196,13 @@ function history_get_range_result_filter( $p_filter, $p_start_time = null, $p_en
 	# Note: filter_get_bug_rows_query_clauses() calls db_param_push();
 	$t_query_clauses = filter_get_bug_rows_query_clauses( $p_filter, null, null, null );
 
+	# if the query can't be formed, there are no results
+	if( empty( $t_query_clauses ) ) {
+		# reset the db_param stack that was initialized by "filter_get_bug_rows_query_clauses()"
+		db_param_pop();
+		return db_empty_result();
+	}
+
 	$t_select_string = 'SELECT DISTINCT {bug}.id ';
 	$t_from_string = ' FROM ' . implode( ', ', $t_query_clauses['from'] );
 	$t_join_string = count( $t_query_clauses['join'] ) > 0 ? implode( ' ', $t_query_clauses['join'] ) : ' ';