If the NERDTree is zoomed when 'o'pening a file, unzoom it.

'go' does not trigger this new behavior, because focus remains in the
NERDTree.

lib/nerdtree/opener.vim

@@ -244,6 +244,9 @@ endfunction
 
 " FUNCTION: Opener._openFile() {{{1
 function! s:Opener._openFile()
+    if !self._stay && exists("b:NERDTreeZoomed") && b:NERDTreeZoomed
+        call b:NERDTree.ui.toggleZoom()
+    endif
 
     if self._reuseWindow()
         return