Fix CSV import for edge with one property (#2175)

- start_index marks where property fields begin. For edges, it's 4.
  If start_index >= total_fields, create empty properties; otherwise,
  parse the properties.

Author: Munmud

src/backend/utils/load/age_load.c

@@ -176,7 +176,7 @@ agtype* create_agtype_from_list_i(char **header, char **fields,
     agtype_in_state result;
     size_t i;
 
-    if (start_index + 1 == fields_len)
+    if (start_index >= fields_len)
     {
         return create_empty_agtype();
     }