Bug in `s:qf_is_open()` fixed
Bug in `s:qf_is_open()` fixed

The `filter()` function accepts a List or Dictionary as the first
argument, so `l:buflist` has to be first transformed into a list by
means of `split()` and then can be passed to `filter()`. (Btw, the former
is executed "in situ" in the latter.)

lervag/vimtex,Aster89/vimtex,kmarius/vimtex,Aster89/vimtex,lervag/vimtex,kmarius/vimtex