Try harder not to choke on broken modeline

Partially addresses #162.

plugin/fugitive.vim

@@ -1283,7 +1283,7 @@ endfunction
 
 call s:add_methods('buffer',['compare_age'])
 
-function! s:Diff(bang,...) abort
+function! s:Diff(bang,...)
   let split = a:bang ? 'split' : 'vsplit'
   if exists(':DiffGitCached')
     return 'DiffGitCached'
@@ -1930,10 +1930,13 @@ function! s:BufReadIndexFile()
   try
     let b:fugitive_type = 'blob'
     let b:git_dir = s:repo().dir()
+    try
       call s:ReplaceCmd(s:repo().git_command('cat-file','blob',s:buffer().sha1()))
+    finally
       if &bufhidden ==# ''
         setlocal bufhidden=delete
       endif
+    endtry
     return ''
   catch /^fugitive: rev-parse/
     silent exe 'doau BufNewFile '.s:fnameescape(bufname(''))
@@ -1998,6 +2001,7 @@ function! s:BufReadObject()
     silent %delete
     setlocal endofline
 
+    try
       if b:fugitive_type == 'tree'
         let b:fugitive_display_format = b:fugitive_display_format % 2
         if b:fugitive_display_format
@@ -2032,6 +2036,7 @@ function! s:BufReadObject()
       elseif b:fugitive_type ==# 'blob'
         call s:ReplaceCmd(s:repo().git_command('cat-file',b:fugitive_type,hash))
       endif
+    finally
       call setpos('.',pos)
       setlocal ro noma nomod
       if &bufhidden ==# ''
@@ -2044,6 +2049,7 @@ function! s:BufReadObject()
       else
         call s:JumpInit()
       endif
+    endtry
 
     return ''
   catch /^fugitive:/