Fix issue apache#1347 - unknow type of agtype container 0 (apache#1349)

The error was caused by the Datum referenced by
edge_entry->edge_properties becoming non-persistent. As a
result, the pointer becomes dangling. This issue is fixed
by making a copy of the Datum into the MemoryContext it is
used. The fix is also applied to
vertex_entry->vertex_properties.

Thanks to John for finding out the correct function to
copy a Datum.

Co-authored-by: John Gemignani <jrgemignani@gmail.com>

src/backend/utils/adt/age_global_graph.c

@@ -25,13 +25,13 @@
 #include "access/table.h"
 #include "access/tableam.h"
 #include "catalog/namespace.h"
+#include "common/hashfn.h"
 #include "commands/label_commands.h"
+#include "utils/datum.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
 #include "utils/snapmgr.h"
-#include "commands/label_commands.h"
-#include "common/hashfn.h"
 
 #include "catalog/ag_graph.h"
 #include "catalog/ag_label.h"
@@ -448,6 +448,8 @@ static void load_vertex_hashtable(GRAPH_global_context *ggctx)
             /* get the vertex properties datum */
             vertex_properties = column_get_datum(tupdesc, tuple, 1,
                                                  "properties", AGTYPEOID, true);
+            /* we need to make a copy of the properties datum */
+            vertex_properties = datumCopy(vertex_properties, false, -1);
 
             /* insert vertex into vertex hashtable */
             inserted = insert_vertex_entry(ggctx, vertex_id,
@@ -561,6 +563,9 @@ static void load_edge_hashtable(GRAPH_global_context *ggctx)
             edge_properties = column_get_datum(tupdesc, tuple, 3, "properties",
                                                AGTYPEOID, true);
 
+            /* we need to make a copy of the properties datum */
+            edge_properties = datumCopy(edge_properties, false, -1);
+
             /* insert edge into edge hashtable */
             inserted = insert_edge(ggctx, edge_id, edge_properties,
                                    edge_vertex_start_id, edge_vertex_end_id,