Admin section: Put validation on sync call to force a match sync from Frenoy

[JornHeyvaert]

It's possible to perform a force match sync towards Frenoy without filling in a match ID on this screen:

This results in a 500 error message because we don't give a match ID as a parameter:

POST http://www.ttc-erembodegem.be/api/matches/FrenoyMatchSync?forceSync=true 500 (Something went terribly wrong!)

Possible quick ideas for enhancement:

• Put validation so that the API call is only made if there is a value filled in in the Match ID
• Disable the 'Force sync' button and enable it when a value has been filled in