py: Fix function calls that have positional and a star-arg-with-iterator.

Addresses issue #1678.

py/runtime.c

@@ -671,6 +671,7 @@ void mp_call_prepare_args_n_kw_var(bool have_self, mp_uint_t n_args_n_kw, const
 
         // copy the fixed position args
         mp_seq_copy(args2 + args2_len, args, n_args, mp_obj_t);
+        args2_len += n_args;
 
         // extract the variable position args from the iterator
         mp_obj_t iterable = mp_getiter(pos_seq);

tests/basics/fun_callstar.py

@@ -14,6 +14,9 @@ foo(1, 2, *[100])
 # Iterator
 foo(*range(3))
 
+# pos then iterator
+foo(1, *range(2, 4))
+
 # method calls with *pos
 
 class A: