Do not redefine refreshCompleterState on each render

[krassowski]

Fixes #874

[dlqqq]

Thanks! This should definitely be more performant, though I don't think the previous version suffered a memory leak; I think the garbage collector will deallocate functions defined at-render.

[krassowski]

The leak was not due to multiple function definitions (that as you say will be freed easily) but due to the signal staying connected (and thus not dispoed) to the old function as the new reference was not matching the reference of redefined function. In any case it was just a tiny leak.