Problem:
Changing from an empty-line cursor after a multicursor jump can crash
while flushing a deferred clipboard update. Exact context restore can
leave an omitted register with a null array and stale non-zero size.
Solution:
Make free_register() fully reset the register after freeing its contents,
so it always leaves a valid empty register. Add a regression test.
Signed-off-by: sami <samiulsami7786@gmail.com>
b7a0c71a54