Prevent a heap pointer from living on the stack longer than we need.

lib/utils/pyexec.c

@@ -90,6 +90,8 @@ STATIC int parse_compile_execute(const void *source, mp_parse_input_kind_t input
             qstr source_name = lex->source_name;
             mp_parse_tree_t parse_tree = mp_parse(lex, input_kind);
             module_fun = mp_compile(&parse_tree, source_name, MP_EMIT_OPT_NONE, exec_flags & EXEC_FLAG_IS_REPL);
+            // Clear the parse tree because it has a heap pointer we don't need anymore.
+            *((uint32_t volatile*) &parse_tree.chunk) = 0;
             #else
             mp_raise_msg(&mp_type_RuntimeError, "script compilation not supported");
             #endif