diff: fix --color-moved-ws=allow-indentation-change

diff: fix --color-moved-ws=allow-indentation-change

If there is more than one potential moved block and the longest block
is not the first element of the array of potential blocks then the
block is cut short. With --color-moved=blocks this can leave moved
lines unpainted if the shortened block does not meet the block length
requirement. With --color-moved=zebra then in addition to the
unpainted lines the moved color can change in the middle of a single
block.

Fix this by freeing the whitespace delta of the match we're discarding
rather than the one we're keeping.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Acked-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>