Always prevent flicker.

Previously flicker was prevented only when the sign column was
always present.

README.mkd

@@ -199,10 +199,6 @@ Note that this is always off with gVim on Windows due to a Vim/shell bug causing
 
 Your colorscheme is configuring the `SignColumn` highlight group weirdly.  Please see the section above on customising the sign column.
 
-> Why does the window flicker when the signs are redrawn?
-
-This happens on certain combinations of OS and Vim.  You can prevent the flicker by adding `let g:gitgutter_sign_column_always = 1` to your `~/.vimrc`.
-
 > There's a noticeable lag when vim-gitter runs; how can I avoid it?
 
 By default vim-gitgutter runs often so the signs are as accurate as possible.  However on some systems this causes a noticeable lag.  If you would like to trade a little accuracy for speed, add one or both of these to your `~/.vimrc`:

plugin/gitgutter.vim

@@ -110,6 +110,10 @@ function! s:is_tracked_by_git()
   return !v:shell_error
 endfunction
 
+function! s:differences(hunks)
+  return len(a:hunks) != 0
+endfunction
+
 function! s:snake_case_to_camel_case(text)
   return substitute(a:text, '\v(.)(\a+)(_(.)(.+))?', '\u\1\l\2\u\4\l\5', '')
 endfunction
@@ -417,6 +421,12 @@ function! GitGutter(file)
     let modified_lines = s:process_hunks(s:hunks)
     if g:gitgutter_sign_column_always
       call s:add_dummy_sign()
+    else
+      if s:differences(s:hunks)
+        call s:add_dummy_sign()  " prevent flicker
+      else
+        call s:remove_dummy_sign()
+      endif
     endif
     call s:clear_signs(a:file)
     call s:find_other_signs(a:file)