Zero-initialize parent_cpstate in analyze_cypher (#2423)

cypher_parsestate parent_cpstate is declared on the stack in
analyze_cypher() and only pstate is explicitly set before it is passed
to make_cypher_parsestate(). The latter reads
parent_cpstate->subquery_where_flag (and other fields) in
cypher_parse_node.c, which leaves them with indeterminate values. UBSan
flagged the garbage bool (value 8) and aborted the backend.

Use MemSet to zero the struct before populating pstate so all remaining
members start with a defined value.

Co-authored-by: Hari Krishna Sunder <12418230+hari90@users.noreply.github.com>

Author: hari90

src/backend/parser/cypher_analyze.c

@@ -961,9 +961,8 @@ static Query *analyze_cypher(List *stmt, ParseState *parent_pstate,
      * convert ParseState into cypher_parsestate temporarily to pass it to
      * make_cypher_parsestate()
      */
+    MemSet(&parent_cpstate, 0, sizeof(parent_cpstate));
     parent_cpstate.pstate = *parent_pstate;
-    parent_cpstate.graph_name = NULL;
-    parent_cpstate.params = NULL;
 
     cpstate = make_cypher_parsestate(&parent_cpstate);