First let me start by saying "Revit Railings are of the Devil". I must say they are by far the worst part of the software. Next, what you have to consider when working with panels is that Revit does not adjust the panel size for you in a railing. (Adding that to my wish list). Whatever the length of the panel family is, is what Revit will show in the system. For example, if you have panels that are 4' long, and you have a railing that's 6' it will not add a single or two smaller panels to the system to make up for the extra 2 feet of length. It will leave those excess lengths empty because your panel size is larger than the remaining railing length. Also, truncating the railing will not work in this case, because again, your panel size is larger than the amount of length you have left over.
I did not download your model, but in the sections you attached I see that you have a couple of options.
1. At the bottom of your run you can split the railing sketch line. Where you've split the line a post will be added. That way at least, it won’t look like your glass panel isn't attached to anything.
2. Your other option is to create additional panel sizes to accommodate the smaller lengths.
When using panels it's always good to map out the length of the railing ahead of time so that you can minimize the "gaps" created by excess length. So if you have 24" panels, try to draw railings in multiples of 2 feet to maximize panels, and minimize gaps.
Hope this helps!