api: fix leak when a api function is incorrectly called with a list.

This applies both to msgpack-rpc and eval.

src/nvim/eval.c

@@ -7140,8 +7140,7 @@ static void api_wrapper(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   }
 
 end:
-  // All arguments were freed already, but we still need to free the array
-  xfree(args.items);
+  api_free_array(args);
   api_free_object(result);
 }
 

src/nvim/msgpack_rpc/channel.c

@@ -465,8 +465,7 @@ static void on_request_event(void **argv)
   } else {
     api_free_object(result);
   }
-  // All arguments were freed already, but we still need to free the array
-  xfree(args.items);
+  api_free_array(args);
   decref(channel);
   xfree(e);
 }