syncthing: update to 0.14.50.

Bugfixes:

    #5038: Repeating INFO: UPnP parse: unrecognized UPnP device of type upnp:rootdevice
    #5063: panic: cannot start already running folder
    #5073: lib/logger: tests fail due to compilation error with go 1.11
    #5089: Invalid files shouldn't affect global state
    #5144: Tests fail on Go 1.11 / Windows
    #5149: Index updates lost

Other issues:

    #3595: stdiscosrv: Doesn't build on Solaris
    #5043: root on symlinked path causes panic when using "Watch for changes"

Also:

This release includes initial support for "receive only" folders.
See https://docs.syncthing.net/users/foldertypes.html#receive-only-folder.

(wiz)