Avoid potential buffer overflow crash

A pointer to a C string was treated as a pointer to a "name" datum and
passed to SPI_execute_plan().  This pointer would then end up being
passed through datumCopy(), which would try to copy the entire 64 bytes
of name data, thus running past the end of the C string.  Fix by
converting the string to a proper name structure.

Found by LLVM AddressSanitizer.

src/backend/utils/adt/ruleutils.c

@@ -428,7 +428,7 @@ pg_get_viewdef_worker(Oid viewoid, int prettyFlags)
 	 * Get the pg_rewrite tuple for the view's SELECT rule
 	 */
 	args[0] = ObjectIdGetDatum(viewoid);
-	args[1] = PointerGetDatum(ViewSelectRuleName);
+	args[1] = DirectFunctionCall1(namein, CStringGetDatum(ViewSelectRuleName));
 	nulls[0] = ' ';
 	nulls[1] = ' ';
 	spirc = SPI_execute_plan(plan_getviewrule, args, nulls, true, 2);