MDL-36606 made changes to the AJAX grader report interface, which break the ctrl+left/right/up/down navigation when the gradebook is in editing mode.

The patch introduced in MDL-36606 looks for a new "clickable" class, but only applies that class when editing mode is off - when editing mode is on, the keyboard navigation functions can't find any cells with the "clickable" class and thus cycle through the table and eventually spit out a JS error along the lines of "TypeError: this.current is null".

The simplest fix is to move the logic which applies the "clickable" class to a location where it runs whether or not the gradebook is in editing mode, so that the class is applied (where appropriate) irrespective of whether editing mode is enabled.