#1798 With new jack transport record position sometimes jumps

[Philip Leishman]

With new jack transport and count in of 2 bars:

1. start Rosegarden.
2. Move cursor to bar 5.
3. Press Record.
   This sometimes works but some times the position jumps into the future.

[Philip Leishman]

As this sometimes works and sometimes not - it seems to be a race condition between threads.