Fix window position error

[ChaojiangLuo]

The window is positioned by client, but it will be placed to center by the place plugin. Set is_positioned to place plugin to avoid this issue.

Signed-off-by: Chaojiang Luo [email protected] Change-Id: I925ced36e9750667afc3c196db98e0e050b3c0c7

Notice: Wayfire's development is temporarily happening in the stabilize-api branch. If you open a pull request for the master branch, it will likely not be merged before the stabilize-api branch is itself merged into master.