py: fix null pointer dereference in mpz.c, fix missing va_end in warning.c
diff --git a/py/warning.c b/py/warning.c
index eae145b..4cdf3b3 100644
--- a/py/warning.c
+++ b/py/warning.c
@@ -38,6 +38,7 @@
     mp_print_str(&mp_plat_print, "Warning: ");
     mp_vprintf(&mp_plat_print, msg, args);
     mp_print_str(&mp_plat_print, "\n");
+    va_end(args);
 }
 
 void mp_emitter_warning(pass_kind_t pass, const char *msg) {