Distinguish between no response and empty response to query

[TheoWinterhalter]

This problem is probably not specific to vscoq (I think it is the same with Proof General) but I believe it is probably solved at the editor level.

Currently when one uses a query like Print or Search which does not fail but does not turn up anything, we simply get no message in the Query output. So whether it's still processing or simply returned nothing is difficult to tell. Even worse, sometimes the Query seems to be buggy and will not show anything at all unless closed and opened again.

[rtetley]

This is a real problem that I've run into while implementing the query panel for VsCoq 2 but I think its a limitation of the coq api. At least for Search. If someone has an idea how to move forward feel free to comment !