always define 'g:vimtex_latexmk_callback_hooks' (#498)
always define 'g:vimtex_latexmk_callback_hooks' (#498)

the variable 'g:vimtex_latexmk_callback_hooks' is referred to in
autoload/vimtex/view.vim, so it needs to be defined also if
'g:vimtex_latexmk_enabled' is false.
Aster89/vimtex,kmarius/vimtex,kmarius/vimtex,lervag/vimtex,Aster89/vimtex,lervag/vimtex