Temporarily restore User Fugitive autocommand

References https://github.com/tpope/vim-fugitive/issues/1441

plugin/fugitive.vim

@@ -279,6 +279,23 @@ function! FugitiveDetect(path) abort
       let b:git_dir = dir
     endif
   endif
+  if !exists('b:git_dir') || !exists('#User#Fugitive')
+    return ''
+  endif
+  if v:version >= 704 || (v:version == 703 && has('patch442'))
+    doautocmd <nomodeline> User Fugitive
+  elseif &modelines > 0
+    let modelines = &modelines
+    try
+      set modelines=0
+      doautocmd User Fugitive
+    finally
+      let &modelines = modelines
+    endtry
+  else
+    doautocmd User Fugitive
+  endif
+  return ''
 endfunction
 
 function! FugitiveVimPath(path) abort