revert: liuchengxu#459 as it breaks multiwindow setup

Author: nodech

autoload/vista/source.vim

@@ -4,8 +4,7 @@
 
 if exists('*bufwinid')
   function! s:GotoSourceWindow() abort
-    let bufid = g:vista.source.bufnr
-    let winid = bufwinid(bufid)
+    let winid = g:vista.source.get_winid()
     if winid != -1
       if win_getid() != winid
         " No use noautocmd here. Ref #362