In `splice_lines`, there is some arithmetic to compute the required
alignment such that future substitutions in a suggestion are aligned
correctly. However, this assumed that the current substitution's span
was only on a single line. In circumstances where this was not true, it
could result in a arithmetic overflow when the substitution's end
column was less than the substitution's start column.
Signed-off-by: David Wood <david.wood@huawei.com>
d2dc0f3b0f