An input formula where the parser crashes

Reported by @fpl

% ltlfilt -f '{ b -> c[*1..]}'
ltlfilt: formula.cc:1249: void spot::fnode::setup_props(spot::op): Assertion `children[0]->is_sere_formula()' failed.
zsh: abort      bin/ltlfilt -f '{ b -> c[*1..]}'