click-drag to select doesn't work if click starts near an intron line

Please re-assign or not as you see fit.

Currently, if I try to click-drag (rubberband) to select, I have to click on empty space that is outside the region of any Glyph. This is often very inconvenient in the case of sequence reads, which are often packed tightly with no space between them. If the user clicks and then begins a drag to select multiple items, it should not matter if there is already a Glyph at the clicked location. The click-drag/rubber-banding interaction should work no matter what.