prevent line from jumping too far away

Hi, 

just adding a little improvement to prevent not intuitive jumps.

Example:
if you start to draw the line in the upper left region of letter Y and drag it to middle (down/right) and than want to start in the upper right region, line will be automatically filled whenever you start dragging from there. 

To prevent this kind of behavior I just added another if statement to the `compare.js` file, which was not shown in videos.