probably bogus conversion to tgba

This was reported by @xblahoud

% ltlcross 'ltl3tela -f %f | autfilt --tgba > %O'  -f 'F((G(a)) | (G((b) | (F(c)))))'
F((G(a)) | (G((b) | (F(c)))))
Running [P0]: ltl3tela -f 'F((G(a)) | (G((b) | (F(c)))))' | autfilt --tgba > 'lcr-o0-PxIRET'
Running [N0]: ltl3tela -f '!(F((G(a)) | (G((b) | (F(c))))))' | autfilt --tgba > 'lcr-o0-5Kv8d4'
Performing sanity checks and gathering statistics...
error: P0*N0 is nonempty; both automata accept the infinite word:
       cycle{!a & !b & !c}

error: some error was detected during the above runs,
       please search for 'error:' messages in the above trace.

Removing the --tgba option gets rid of the issue.