Prevent plugin from entering shuffling round when it has insufficient funds

[checksum0]

Currently, the plugin will try to enter a shuffle if a shuffler has unconfirmed outputs to shuffle, resulting in a insufficient fund blame. Make sure plugin behavior prevent this from doing so.

Exception in thread Thread-67:
Traceback (most recent call last):
File "C:\Users\iande\AppData\Local\Programs\Python\Python36-32\lib\threading.py", line 916, in _bootstrap_inner
self.run()
File "C:\Users\iande\AppData\Local\Programs\Python\Python36-32\lib\threading.py", line 864, in run
self._target(*self._args, **self._kwargs)
File "D:\fresh\Electron Cash-3.0\plugins\shuffle\coin_shuffle.py", line 206, in protocol_definition
self.blame_insufficient_funds()
File "D:\fresh\Electron Cash-3.0\plugins\shuffle\coin_shuffle.py", line 121, in blame_insufficient_funds
raise BlameException('Insufficient funds')
electroncash_plugins.shuffle.coin_shuffle.BlameException: Insufficient funds

[clifordsymack]

This exception arise when some player from pool have unsufficient funds. Shuffle button will not be enbled if player have insufficient fund, but you can't check other players funds before protocol started

[checksum0]

I agree, but this arose from somebody using the plugin with unconfirmed funds, so leading to the round failing. I agree the server can't check it but the plugin should prevent the users from entering the round if their funds is unconfirmed.