systemctl: it's probably a good idea not to alter return parameters if we fail

We generally follow the rule not to touch return values unless we
succeed, so for the sake of uniformity do the same here.

src/systemctl/systemctl.c

@@ -842,8 +842,9 @@ static int list_dependencies_get_dependencies(DBusConnection *bus, const char *n
         }
 finish:
         if (r < 0)
-                strv_freep(&ret);
-        *deps = ret;
+                strv_free(ret);
+        else
+                *deps = ret;
         return r;
 }