xstate: Ignore Window/Drawable errors

Sometimes, windows will have actually been destroyed before we even
processed the events for it, so if we try to do something like get
properties on windows (as we do whenever a window is mapped) we will get
an error from the X server, but this is fine - we can just ignore this.

Should fix #16, #20, #22, etc.

src/server/mod.rs

@@ -511,6 +511,7 @@ impl<C: XConnection> ServerState<C> {
                     debug!("skipping setting window name to {name:?} because a _NET_WM_NAME title is already set");
                     None
                 } else {
+                    debug!("setting {window:?} title to {name:?}");
                     *w = name;
                     Some(w)
                 }