This used to happen by itself as the connecting device always sent an
Index message and we triggered on that. Nowadays there's no guarantee
for that, but we anyway need to send out one event to let listeners know
the state of folders shared with the device.
GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3438
Without this the summary service doesn't know to recalculate completion
percentage for remote devices when DownloadProgress messages come in.
That means that completion percentage isn't updated in the GUI while
transfers of large files are ongoing. With this change, it updates
correctly.
GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3144
