Code review comment for lp:~trb143/openlp/bug-892571

Well If I use a mutex it locks up.
Without a major (2-3 month) re-write of the code path as it is very long and impacts plugins etc I am not sure what else to try.
The code
   looks up the current selected service item
   Selects the next one.
   Flushes the events to add a cursor
   Adds a service item
   This signals plugins twice to turn off and then hand new service item.
   selects the next service item to preview it.
   Flushes the events to remove the cursor

The Keyboard will start this flow BEFORE the previous has finished so you get a number of calling chains running at the same time.