Refine 'refresh_windows' and Fix 'start_all'

* refine 'refresh_windows' from #364

  - looks should try to refresh all active buf in cur tab -but not just cur one

  - looks better use common func -but not dup code again

  - and modify sy#buffer_is_active() as per jamessan's advice

* fix 'start_all'

  - looks missed '$' in bufnr()

Author: Shane-XB-Qian

autoload/sy.vim

@@ -88,7 +88,7 @@ endfunction
 
 " #start_all {{{1
 function! sy#start_all() abort
-  for bufnr in range(1, bufnr(''))
+  for bufnr in range(1, bufnr("$"))
     call sy#start({'bufnr': bufnr})
   endfor
   let g:signify_disable_by_default = 0
@@ -105,8 +105,9 @@ function! sy#stop_all() abort
 endfunction
 
 " #buffer_is_active {{{1
-function! sy#buffer_is_active()
-  return !empty(getbufvar(bufnr(''), 'sy'))
+function! sy#buffer_is_active(...)
+  let bufnr = a:0 ? a:1 : bufnr('')
+  return !empty(getbufvar(bufnr, 'sy'))
 endfunction
 
 " #verbose {{{1

autoload/sy/util.vim

@@ -24,10 +24,6 @@ endfunction
 
 " #refresh_windows {{{1
 function! sy#util#refresh_windows() abort
-  " return if signify is not active
-  if empty(getbufvar(bufnr(''), 'sy'))
-    return
-  endif
   if exists('*win_getid')
     let winid = win_getid()
   else
@@ -36,7 +32,9 @@ function! sy#util#refresh_windows() abort
 
   if !get(g:, 'signify_cmdwin_active')
     for bufnr in tabpagebuflist()
-      call sy#start({'bufnr': bufnr})
+      if sy#buffer_is_active(bufnr)
+        call sy#start({'bufnr': bufnr})
+      endif
     endfor
   endif