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

This applies both to msgpack-rpc and eval.

scripts/gendispatch.lua

@@ -293,14 +293,8 @@ for i = 1, #functions do
     if fn.return_type ~= 'void' then
       output:write('\n  ret = '..string.upper(real_type(fn.return_type))..'_OBJ(rv);')
     end
-    -- Now generate the cleanup label for freeing memory allocated for the
-    -- arguments
     output:write('\n\ncleanup:');
 
-    for j = 1, #fn.parameters do
-      local param = fn.parameters[j]
-      output:write('\n  api_free_'..string.lower(real_type(param[1]))..'(arg_'..j..');')
-    end
     output:write('\n  return ret;\n}\n\n');
   end
 end

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);
 }

test/functional/api/vim_spec.lua

@@ -303,4 +303,11 @@ describe('vim_* functions', function()
     eq(false, status)
     ok(err:match('Invalid option name') ~= nil)
   end)
+
+  it("doesn't leak memory on incorrect argument types", function()
+    local status, err = pcall(nvim, 'change_directory',{'not', 'a', 'dir'})
+    eq(false, status)
+    ok(err:match(': Wrong type for argument 1, expecting String') ~= nil)
+  end)
+
 end)