Make linedef 96 apply to tags from 97-99, but not to itself

Fixes the first problem in #662 (closed), allowing 96 to point to 97-99. However, 96's still may not be chained together as decided in that issue, so the issue can be closed.

Some people said that the 96 loop should be before the 97-99 loop to keep it simple instead of after, like this MR. I personally think that there's no need to restrict 96 from pointing to 97-99; ideally, we should pretend that 97-99 really are just extra tag fields on the sector just like UDMF, and not anything special. It adds no extra complexity to do it this way, and this is the only difference code-wise:

// This way:
// 97-99 loop
// 96 loop

// Other proposed 96 pointing to 97-99:
// 96 loop
// 97-99

I can flip it anyway if people think it should be that way.

A basic testing map is here: applyfix.wad

(A note: I only really rearranged code, but the diff is easier to understand with whitespace changes ignored, i.e. git diff -w)