Allow creation of empty collections

We've gone back and forth as to whether we should save empty folders or
not. Long-term it seems like we should be. This starts this process (and
simplifies some of the logic). Empty folders will not be able to be
restored without further changes though as they are not directly
accessible through backup details.

src/internal/connector/onedrive/collections.go

@@ -640,24 +640,19 @@ func (c *Collections) UpdateCollections(
 			}
 
 			if !found {
-				// We only create collections for folder that are not
-				// new. This is so as to not create collections for
-				// new folders without any files within them.
-				if prevPath != nil {
-					col := NewCollection(
-						c.itemClient,
-						folderPath,
-						prevPath,
-						driveID,
-						c.service,
-						c.statusUpdater,
-						c.source,
-						c.ctrl,
-						invalidPrevDelta,
-					)
-					c.CollectionMap[*item.GetId()] = col
-					c.NumContainers++
-				}
+				col := NewCollection(
+					c.itemClient,
+					folderPath,
+					prevPath,
+					driveID,
+					c.service,
+					c.statusUpdater,
+					c.source,
+					c.ctrl,
+					invalidPrevDelta,
+				)
+				c.CollectionMap[*item.GetId()] = col
+				c.NumContainers++
 			}
 
 			if c.source != OneDriveSource {
@@ -743,14 +738,6 @@ func (c *Collections) UpdateCollections(
 				if !removed {
 					return clues.New("removing from prev collection").With("item_id", *item.GetId())
 				}
-
-				// If that was the only item in that collection and is
-				// not getting added back, delete the collection
-				if itemColID != collectionID &&
-					pcollection.IsEmpty() &&
-					pcollection.State() == data.NewState {
-					delete(c.CollectionMap, itemColID)
-				}
 			}
 
 			itemCollection[*item.GetId()] = collectionID