Fixed #430: Allow manual enabling of folding

autoload/vimtex/fold.vim

@@ -40,12 +40,14 @@ endfunction
 
 " }}}1
 function! vimtex#fold#init_buffer() " {{{1
+  " b:vimtex_fold is a dictionary used to store dynamic fold information
+  " Note: We define this even if folding is disabled, because people might want
+  "       to enable folding manually
+  let b:vimtex_fold = {}
+
   if !g:vimtex_fold_enabled | return | endif
   if s:foldmethod_in_modeline() | return | endif
 
-  " Initialize local work vars
-  let b:vimtex_fold = {}
-
   " Set fold options
   setlocal foldmethod=expr
   setlocal foldexpr=vimtex#fold#level(v:lnum)