avoid injection in input prompt

IPython/html/static/notebook/js/codecell.js

@@ -409,7 +409,12 b' var IPython = (function (IPython) {'
 
 
     CodeCell.input_prompt_classical = function (prompt_value, lines_number) {
-        var ns = prompt_value || " ";
+        var ns;
+        if (prompt_value == undefined) {
+            ns = " ";
+        } else {
+            ns = encodeURIComponent(prompt_value);
+        }
         return 'In [' + ns + ']:';
     };