[hardwrap addon] Don't generate null changes

Issue #3548

addon/wrap/hardwrap.js

@@ -86,7 +86,8 @@
     if (changes.length) cm.operation(function() {
       for (var i = 0; i < changes.length; ++i) {
         var change = changes[i];
-        cm.replaceRange(change.text, change.from, change.to);
+        if (change.text || CodeMirror.cmpPos(change.from, change.to))
+          cm.replaceRange(change.text, change.from, change.to);
       }
     });
     return changes.length ? {from: changes[0].from, to: CodeMirror.changeEnd(changes[changes.length - 1])} : null;