Fix: the loading condition for fugitive is wrong

We should load fugitive in the following two situations:

+ When we open nvim in a Git repository
+ When we are inside nvim and change the working directory to a Git
  reposity

autoload/utils.vim

@@ -145,3 +145,17 @@ function! utils#Get_titlestr() abort
 
   return l:title_str
 endfunction
+
+" Check if we are inside a Git repo.
+function! utils#Inside_git_repo() abort
+  let res = system('git rev-parse --is-inside-work-tree')
+  if match(res, 'true') == -1
+    return v:false
+  else
+    " Manually trigger a speical user autocmd InGitRepo (to use it for
+    " lazyloading of fugitive by packer.nvim).
+    " See also https://github.com/wbthomason/packer.nvim/discussions/534.
+    doautocmd User InGitRepo
+    return v:true
+  endif
+endfunction