Prevent CoqIDE from hanging when invalid channels are still open.
Prevent CoqIDE from hanging when invalid channels are still open.

This behaviour happens as a sub-bug of #10169 for instance.

JasonGross/coq,Zimmi48/coq,silene/coq,JasonGross/coq,SkySkimmer/coq,SkySkimmer/coq,Zimmi48/coq,coq/coq,ejgallego/coq,ejgallego/coq,SkySkimmer/coq,ejgallego/coq,gares/coq,Zimmi48/coq,Zimmi48/coq,gares/coq,gares/coq,silene/coq,coq/coq,gares/coq,JasonGross/coq,SkySkimmer/coq,JasonGross/coq,ejgallego/coq,coq/coq,silene/coq,gares/coq,coq/coq