visual mode re-highlight fix

-switching from and then back to the peekaboo buffer via multiple
`wincmd p` operations fails, possibly due to the use of option
`bufhidden` in its creation, meaning its never present in the buffer
list
-instead, record window number and reset following the `gv` operation
-bug likely went unnoticed because the side-effects of latter
buffer modifications aren't that noticeable. however, should the
multiple `wincmd p` operations land you on a buffer with
`modifiable=0` set, then a very visible:

 `E21: Cannot make changes,'modifiable' is off`

error is presented, and the operation a user is attempting (e.g.
"+y etc.) fails ..then you know about it!

Author: elbeardmorez

autoload/peekaboo.vim

@@ -115,10 +115,11 @@ endfunction
 " Triggers gv to keep visual highlight on
 function! s:gv(visualmode, visible)
   if a:visualmode && a:visible
+    let wnr = bufwinnr('')
     wincmd p
     normal! gv
     redraw
-    wincmd p
+    execute wnr 'wincmd w'
   else
     redraw
   endif