lib/model: Use the new file name when requesting rescan

If the file is not already in the database, the "curfile" will be empty
and the rescan request cover the entire folder.

lib/model/rwfolder.go

@@ -1386,7 +1386,7 @@ func (f *sendReceiveFolder) performFinish(state *sharedPullerState) error {
 			// sweep is complete. As we do retries, we'll queue the scan
 			// for this file up to ten times, but the last nine of those
 			// scans will be cheap...
-			go f.Scan([]string{state.curFile.Name})
+			go f.Scan([]string{state.file.Name})
 			return fmt.Errorf("file modified but not rescanned; will try again later")
 		}