Prevent bad modeline from blocking a :split

Closes https://github.com/tpope/vim-fugitive/issues/1136

autoload/fugitive.vim

@@ -1345,7 +1345,6 @@ function! s:ReplaceCmd(cmd, ...) abort
   endif
   let temp = s:Resolve(temp)
   let fn = expand('%:p')
-  silent exe 'doau BufReadPre '.s:fnameescape(fn)
   silent exe 'keepalt file '.temp
   let modelines = &modelines
   try
@@ -1365,7 +1364,6 @@ function! s:ReplaceCmd(cmd, ...) abort
     if s:cpath(fnamemodify(bufname('$'), ':p'), temp)
       silent execute 'bwipeout '.bufnr('$')
     endif
-    silent exe 'doau BufReadPost '.s:fnameescape(fn)
   endtry
 endfunction
 
@@ -1377,6 +1375,7 @@ function! fugitive#BufReadStatus() abort
   let b:fugitive_display_format = b:fugitive_display_format % 2
   let b:fugitive_type = 'index'
   try
+    silent doautocmd BufReadPre
     let cmd = [fnamemodify(amatch, ':h')]
     setlocal noro ma nomodeline
     if s:cpath(fnamemodify($GIT_INDEX_FILE !=# '' ? $GIT_INDEX_FILE : b:git_dir . '/index', ':p')) !=# s:cpath(amatch)
@@ -1446,6 +1445,7 @@ function! fugitive#BufReadStatus() abort
     nnoremap <buffer>          . : <C-R>=<SID>fnameescape(<SID>StatusCfile())<CR><Home>
     nnoremap <buffer> <silent> g?   :help fugitive-:Gstatus<CR>
     nnoremap <buffer> <silent> <F1> :help fugitive-:Gstatus<CR>
+    return 'silent doautocmd BufReadPost'
   catch /^fugitive:/
     return 'echoerr v:errmsg'
   endtry
@@ -1521,7 +1521,7 @@ function! fugitive#BufReadCmd(...) abort
         unlet b:fugitive_type
         if rev =~# '^:\d:'
           let &readonly = !filewritable(dir . '/index')
-          return 'silent doautocmd BufNewFile '.s:fnameescape(amatch)
+          return 'silent doautocmd BufNewFile'
         else
           setlocal readonly nomodifiable
           return 'echo ' . string(error)
@@ -1544,6 +1544,7 @@ function! fugitive#BufReadCmd(...) abort
     setlocal endofline
 
     try
+      silent doautocmd BufReadPre
       if b:fugitive_type ==# 'tree'
         let b:fugitive_display_format = b:fugitive_display_format % 2
         if b:fugitive_display_format
@@ -1584,17 +1585,12 @@ function! fugitive#BufReadCmd(...) abort
         call s:ReplaceCmd([dir, 'ls-files', '--stage'])
       elseif b:fugitive_type ==# 'blob'
         call s:ReplaceCmd([dir, 'cat-file', b:fugitive_type, rev])
-        setlocal nomodeline
       endif
     finally
       keepjumps call setpos('.',pos)
       setlocal nomodified noswapfile
-      if rev !~# '^:.:'
-        setlocal nomodifiable
-      else
-        let &modifiable = b:fugitive_type !=# 'tree'
-      endif
-      let &readonly = !&modifiable || !filewritable(dir . '/index')
+      let modifiable = rev =~# '^:.:' && b:fugitive_type !=# 'tree'
+      let &readonly = !modifiable || !filewritable(dir . '/index')
       if &bufhidden ==# ''
         setlocal bufhidden=delete
       endif
@@ -1607,7 +1603,8 @@ function! fugitive#BufReadCmd(...) abort
       endif
     endtry
 
-    return ''
+    return 'silent doautocmd' . (v:version >= 704 ? ' <nomodeline>' : '') .
+          \ ' BufReadPost' . (modifiable ? '' : '|setl nomodifiable')
   catch /^fugitive:/
     return 'echoerr v:errmsg'
   endtry