Treat window without type like normal window

Some windows do not specify any `_NET_WM_WINDOW_TYPE`. In that case
treat them like normal windows. It is expected that creaters of special
windows are more concious about setting this property correctly. Normal
developers may be unaware and are more likely not to specify the type.

E.g. Official Spotify does not have a `_NET_WM_WINDOW_TYPE` in the
latest version.

src/sources/windows.rs

@@ -19,13 +19,14 @@ impl Window {
 
     fn is_normal_window(&self, con: &ewmh::Connection, window: u32) -> Result<bool, xcb::GenericError> {
         let wm_type_reply = ewmh::get_wm_window_type(con, window).get_reply()?;
+
         for atom in wm_type_reply.atoms() {
             if *atom == con.WM_WINDOW_TYPE_NORMAL() {
                 return Ok(true);
             }
         }
 
-        Err(xcb::GenericError{ptr: ptr::null_mut()})
+        Ok(false)
     }
 
     fn window_category(&self, con: &ewmh::Connection, window: u32) -> Result<String, xcb::GenericError> {
@@ -94,7 +95,7 @@ impl Source for Window {
             match self.is_normal_window(&ewmh_conn, *w) {
                 Ok(true) => {},
                 Ok(false) => continue,
-                Err(_err) => continue
+                Err(_err) => {}
             }
 
             let title = self.window_title(&ewmh_conn, *w).unwrap();