safer way to check if tabSize pref has been retrieved

Author: redmunds

src/editor/Editor.js

@@ -878,13 +878,13 @@ define(function (require, exports, module) {
      */
     Editor.prototype.getColOffset = function (pos) {
         var line    = this._codeMirror.getRange({line: pos.line, ch: 0}, pos),
-            tabSize,
+            tabSize = null,
             column  = 0,
             i;
 
         for (i = 0; i < line.length; i++) {
             if (line[i] === '\t') {
-                if (!tabSize) {
+                if (tabSize === null) {
                     tabSize = Editor.getTabSize();
                 }
                 column += (tabSize - (column % tabSize));