Quit if no more normal window exists

There might be other plugin windows but no normal file window open, we
need to make sure tagbar window is closed at this situation.

autoload/tagbar.vim

@@ -3359,7 +3359,7 @@ endfunction
 " s:QuitIfOnlyWindow() {{{2
 function! s:QuitIfOnlyWindow() abort
     " Check if there is more than window
-    if winbufnr(2) == -1
+    if s:NextNormalWindow() == -1
         " Check if there is more than one tab page
         if tabpagenr('$') == 1
             " Before quitting Vim, delete the tagbar buffer so that
@@ -3372,6 +3372,41 @@ function! s:QuitIfOnlyWindow() abort
     endif
 endfunction
 
+" s:NextNormalWindow() {{{2
+fun! s:NextNormalWindow()
+    let l:i = 1
+    while(l:i <= winnr('$'))
+        let l:buf = winbufnr(l:i)
+
+        " skip unlisted buffers
+        if buflisted(l:buf) == 0
+            let l:i = l:i + 1
+            continue
+        endif
+
+        " skip un-modifiable buffers
+        if getbufvar(l:buf, '&modifiable') != 1
+            let l:i = l:i + 1
+            continue
+        endif
+
+        " skip temporary buffers with buftype set
+        if empty(getbufvar(l:buf, "&buftype")) != 1
+            let l:i = l:i + 1
+            continue
+        endif
+
+        " skip current normal window
+        if l:i == winnr()
+            let l:i = l:i + 1
+            continue
+        endif
+
+        return l:i
+    endwhile
+    return -1
+endfun
+
 " s:winexec() {{{2
 function! s:winexec(cmd) abort
     call s:LogDebugMessage("Executing without autocommands: " . a:cmd)