Remove unnecessary use of DOC_VALID() macro.

git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@5656 ea778897-0a13-0410-b9d1-a72fbfd435f5

plugins/splitwindow.c

@@ -447,7 +447,7 @@ static gboolean do_select_current(gpointer data)
 		return FALSE;
 
 	doc = document_get_current();
-	if (DOC_VALID(doc))
+	if (doc)
 		set_editor(&edit_window, doc->editor);
 	else
 		on_unsplit(NULL, NULL);