Add explanatory comment about creating a new list each time

Author: KevinBoulongne

Diff for: app/src/main/java/com/infomaniak/mail/ui/main/thread/ThreadViewModel.kt

@@ -252,11 +252,13 @@ class ThreadViewModel @Inject constructor(
 
             val batch = input.take(batchSize)
             output.addAll(batch)
-            batchedMessages.postValue(output.toMutableList())
-            if (batch.size < batchSize) return
 
-            delay(50L)
+            // We need to post a different list each time, because the `submitList` function
+            // in AsyncListDiffer won't trigger if we send the same list object.
+            batchedMessages.postValue(ArrayList(output))
 
+            if (batch.size < batchSize) return
+            delay(50L)
             sendBatchesRecursively(input.subList(batchSize, input.size), output)
         }