DevTools: [Console] fix corner case in viewport text selection

Source/devtools/front_end/ui/ViewportControl.js

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 491 matching lines @@
     },
 
     /**
      * @param {!Element} itemElement
      * @param {!Node} container
      * @param {number} offset
      * @return {number}
      */
     _textOffsetInNode: function(itemElement, container, offset)
     {
-        if (!offset)
-            return 0;
         var chars = 0;
         var node = itemElement;
         while ((node = node.traverseNextTextNode()) && node !== container)
             chars += node.textContent.length;
         return chars + offset;
     },
 
     /**
      * @param {!Event} event
      */
@@ skipping 68 matching lines @@
 
     /**
      * @return {number}
      */
     _visibleHeight: function()
     {
         // Use offsetHeight instead of clientHeight to avoid being affected by horizontal scroll.
         return this.element.offsetHeight;
     }
 }