fix(wm): handle monitor index pref edge case

This commit handles an edge case where the first registered display
monitor has an index preference that is greater than the current length
of the Ring data structure storing the monitors.

re #612

komorebi/src/windows_callbacks.rs

@@ -110,14 +110,16 @@ pub extern "system" fn enum_display_monitor(
 
         let display_index_preferences = DISPLAY_INDEX_PREFERENCES.lock();
         for (index, device) in &*display_index_preferences {
-            if let Some(known_device) = m.device() {
+            if let Some(known_device) = m.device_id() {
                 if device == known_device {
                     index_preference = Option::from(index);
                 }
             }
         }
 
-        if let Some(preference) = index_preference {
+        if monitors.elements().is_empty() {
+            monitors.elements_mut().push_back(m);
+        } else if let Some(preference) = index_preference {
             let current_len = monitors.elements().len();
             if *preference > current_len {
                 monitors.elements_mut().reserve(1);