refactor(event cache): add first_chunk_as_gap() in EventLinkedChunk too

crates/matrix-sdk/src/event_cache/room/event_focused.rs

@@ -277,16 +277,8 @@ impl EventFocusedCacheInner {
     }
 
     /// Return the first chunk as a gap, if it's one.
-    ///
-    /// This stores the backward pagination token, in this case.
     fn first_chunk_as_gap(&self) -> Option<(ChunkIdentifier, Gap)> {
-        self.chunk.chunks().next().and_then(|chunk| {
-            if let ChunkContent::Gap(gap) = chunk.content() {
-                Some((chunk.identifier(), gap.clone()))
-            } else {
-                None
-            }
-        })
+        self.chunk.first_chunk_as_gap()
     }
 
     /// Return the last chunk as a gap, if it's one.

crates/matrix-sdk/src/event_cache/room/events.rs

@@ -507,6 +507,17 @@ impl EventLinkedChunk {
 
         replaced_some
     }
+
+    /// Return the first chunk as a gap, if it's one.
+    pub fn first_chunk_as_gap(&self) -> Option<(ChunkIdentifier, Gap)> {
+        self.chunks().next().and_then(|chunk| {
+            if let ChunkContent::Gap(gap) = chunk.content() {
+                Some((chunk.identifier(), gap.clone()))
+            } else {
+                None
+            }
+        })
+    }
 }
 
 // Methods related to lazy-loading.