No Quick View preview past end of line

This is for issue #5102.

This also fixes a color preview bug I noticed (which was introduced by my recent performance changes):

1. Paste this rule in a style sheet
```
.main {
    color: red; color: blue; background-image: -o-linear-gradient(#ffefaa,#ffe155); background-color: #333;
}
```
2. Move mouse over colors

Result:
Colors before gradient displays incorrect color (i.e. the gradient). Color after gradient displays correct color.