Fix segfault in tsk_variant_restricted_copy

[jeromekelleher]

Incorrect buffer size calculations caused segfault when long alleles are present.

Closes #2429

[jeromekelleher]

This fixes the issue as simply as possible (and underlines the advantages of using the x= malloc(size * sizeof(*x)); pattern), however I think we can do things more simply and robustly by using a proper state machine for the variant class (#2436). We can do this as a follow up once the immediate segfault has been fixed, and released.

[codecov]

Codecov Report

Merging #2437 (8e87bfd) into main (8e87bfd) will not change coverage.
The diff coverage is n/a.

❗ Current head 8e87bfd differs from pull request most recent head 1690069. Consider uploading reports for the commit 1690069 to get more accurate results

@@           Coverage Diff           @@
##             main    #2437   +/-   ##
=======================================
  Coverage   93.43%   93.43%           
=======================================
  Files          28       28           
  Lines       27346    27346           
  Branches     1253     1253           
=======================================
  Hits        25550    25550           
  Misses       1762     1762           
  Partials       34       34           

Flag	Coverage Δ
c-tests	92.26% <0.00%> (ø)
lwt-tests	89.05% <0.00%> (ø)
python-c-tests	71.39% <0.00%> (ø)
python-tests	98.95% <0.00%> (ø)

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[benjeffery]

LGTM!