[depthFirstSearch] Returning empty rows in case of empty edges_sql query

Author: krashish8

src/depthFirstSearch/depthFirstSearch.c

@@ -71,6 +71,12 @@ process(
     pgr_get_edges(edges_sql, &edges, &total_edges);
     PGR_DBG("Total edges in query %ld", total_edges);
 
+    if (total_edges == 0) {
+        if (rootsArr) pfree(rootsArr);
+        pgr_SPI_finish();
+        return;
+    }
+
     PGR_DBG("Starting processing");
     clock_t start_t = clock();
     char *log_msg = NULL;

src/depthFirstSearch/depthFirstSearch_driver.cpp

@@ -67,6 +67,7 @@ do_pgr_depthFirstSearch(
         pgassert(!(*err_msg));
         pgassert(!(*return_tuples));
         pgassert(*return_count == 0);
+        pgassert(total_edges != 0);
 
         std::vector<int64_t> roots(rootsArr, rootsArr + size_rootsArr);