chore(sdk): Improve an inline comment.

Author: Hywan

crates/matrix-sdk/src/event_cache/caches/thread/pagination.rs

@@ -114,7 +114,8 @@ impl PaginatedCache for ThreadEventCacheWrapper {
 
         let prev_first_chunk = state.thread_linked_chunk().first_chunk();
 
-        // The first chunk is not a gap, we can load its previous chunk.
+        // If we are here, it means all gaps have been resolved (see the `if` block
+        // above). So the first chunk is not a gap, we can load its previous chunk.
         let linked_chunk_id = LinkedChunkId::Thread(&state.room_id, &state.thread_id);
         let new_first_chunk = match state
             .store