frame: projection: hard-coded magic numbers can underflow for long lines

[as]

Under certain conditions a hard-coded constant is used to calculate the 1-D x-max point at the end of the frame. If the actual number of characters in the frame exceeds this limit some rendering operations may be limited to the value of the constant.

This is an issue primarily for extremely long runs of text missing hard newline characters.

as/frame/delete.go:133: pt2 := f.pointOf(65536, pt1, n1)