[LiveIntervals] Fix early-clobber handling in handleMoveUp

Without this fix, handleMoveUp can create an invalid live range like
this:

[98904e,98908r:0)[98908e,227504r:1)

where the two segments overlap, but only because we have lost the "e"
(early-clobber) on the end point of the first segment.

Differential Revision: https://reviews.llvm.org/D82110