Fix small timeline bug when defining timeline with no options and fix docs explanations

docs/timeline/index.html

@@ -680,7 +680,7 @@ <h2 id="Configuration_Options">Configuration Options</h2>
       <td>Boolean</td>
       <td>false</td>
       <td>This option allows you to scroll horizontally to move backwards and forwards in the time range.
-       Only applicable when option <code>zoomCtrl</code> is defined or <code>zoomable</code> is <code>false</code>.
+       Only applicable when option <code>zoomCtrl</code> is defined or <code>zoomable</code> is <code>false</code>. Notice that defining this option as <code>true</code> will override <code>verticalScroll</code> scroll event but not eliminate the vertical scrollbar.
       </td>
     </tr>
 
@@ -1028,7 +1028,7 @@ <h2 id="Configuration_Options">Configuration Options</h2>
       <td>verticalScroll</td>
       <td>Boolean</td>
       <td>false</td>
-      <td> Show a vertical scroll on the side of the group list.    
+      <td> Show a vertical scroll on the side of the group list and link it to the scroll event when zoom is not triggered. Notice that defining this option as <code>true</code> will NOT override <code>horizontalScroll</code>. The scroll event will be vertically ignored, but a vertical scrollbar will be visible    
       </td>
     </tr>
 

lib/timeline/Timeline.js

@@ -60,7 +60,7 @@ function Timeline (container, items, groups, options) {
     minHeight: null
   };
   this.options = util.deepExtend({}, this.defaultOptions);
-  this.options.rtl = options.rtl;
+  if (options) { this.options.rtl = options.rtl; }
 
   // Create the DOM, props, and emitter
   this._create(container);