Fix COPY_TMP live range construction with optimization

The use may be optimized away, leaving us only with the free use.
Also fix off-by-one error in the other optimization case.

Typo

Fix COPY_TMP live range construction after optimization

If we optimize the FREE away, we should switch to constructing
a normal live range, rather than a split live range.

Fixes

Fix COPY_TMP live range construction after optimization

If we optimize the FREE away, we should switch to constructing
a normal live range, rather than a split live range.

Fixes oss-fuzz #39548.

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