man.vim: never switch to non-man window #11286

In order to find if there was already an open man page, the :Man command
would cycle through each window to see if &ft=='man'. This triggers
autocmds, e.g. BufEnter, unnecessarily and can have unexpected
side-effects.

Change the logic to check each window's ft without switching to it
unless it is actually a man window.

Signed-off-by: Joshua Rubin <me@jawa.dev>

runtime/autoload/man.vim

@@ -284,20 +284,16 @@ function! s:extract_sect_and_name_path(path) abort
 endfunction
 
 function! s:find_man() abort
-  if &filetype ==# 'man'
-    return 1
-  elseif winnr('$') ==# 1
-    return 0
-  endif
-  let thiswin = winnr()
-  while 1
-    wincmd w
-    if &filetype ==# 'man'
+  let l:win = 1
+  while l:win <= winnr('$')
+    let l:buf = winbufnr(l:win)
+    if getbufvar(l:buf, '&filetype', '') ==# 'man'
+      execute l:win.'wincmd w'
       return 1
-    elseif thiswin ==# winnr()
-      return 0
     endif
+    let l:win += 1
   endwhile
+  return 0
 endfunction
 
 function! s:error(msg) abort