Add check for MediaPoolItem existence before processing. Improve data handling in timeline items retrieval function.

- Added a check to skip processing if MediaPoolItem doesn't exist.
- Enhanced data handling within the timeline items retrieval function.
- this is for case some adjustment clips or fusion clips are on timeline

client/ayon_core/hosts/resolve/api/lib.py

@@ -409,6 +409,9 @@ def get_current_timeline_items(
         }
         # get track item object and its color
         for clip_index, ti in enumerate(_clips[track_index]):
+            if not ti.GetMediaPoolItem():
+                continue
+
             data = _data.copy()
             data["clip"] = {
                 "item": ti,