objfun: Fix default arguments filling loop, was broken in presense of kwargs.

py/objfun.c

@@ -299,9 +299,9 @@ continue2:;
         // Now fill in defaults
         mp_obj_t *d = &flat_args[self->n_args - 1];
         mp_obj_t *s = &self->extra_args[self->n_def_args - 1];
-        for (int i = self->n_def_args; i > 0; i--) {
+        for (int i = self->n_def_args; i > 0; i--, d--, s--) {
             if (*d == MP_OBJ_NULL) {
-                *d-- = *s--;
+                *d = *s;
             }
         }
         DEBUG_printf("Args after filling defaults: ");

tests/basics/fun-defargs2.py

@@ -11,3 +11,9 @@ foo(1, b=333)
 
 # override with keyword
 foo(a=2, b=333)
+
+def foo2(a=1, b=2):
+    print(a, b)
+
+# default and keyword
+foo2(b='two')