clear In[ ] prompt numbers again

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

@@ -247,9 +247,7 b' var IPython = (function (IPython) {'
         if( this.code_mirror != undefined) {
            nline = this.code_mirror.lineCount();
         }
-        if (number){
-            this.input_prompt_number = number;
-        }
+        this.input_prompt_number = number;
         var prompt_html = CodeCell.input_prompt_function(this.input_prompt_number, nline);
         this.element.find('div.input_prompt').html(prompt_html);
     };