Also don't let HTML and dependent syntaxes change 'foldmethod'

References https://github.com/tpope/vim-markdown/issues/154

syntax/markdown.vim

@@ -12,12 +12,13 @@ if !exists('main_syntax')
   let main_syntax = 'markdown'
 endif
 
-runtime! syntax/html.vim
-unlet! b:current_syntax
-
 if has('folding')
   let s:foldmethod = &l:foldmethod
 endif
+
+runtime! syntax/html.vim
+unlet! b:current_syntax
+
 if !exists('g:markdown_fenced_languages')
   let g:markdown_fenced_languages = []
 endif
@@ -35,8 +36,10 @@ for s:type in map(copy(g:markdown_fenced_languages),'matchstr(v:val,"[^=]*$")')
 endfor
 unlet! s:type
 unlet! s:done_include
+
 if exists('s:foldmethod') && s:foldmethod !=# &l:foldmethod
   let &l:foldmethod = s:foldmethod
+  unlet s:foldmethod
 endif
 
 if !exists('g:markdown_minlines')