Fix buffer overflow when opening the Fit Panel

[langufo]

Fedora 40 build for 6.32.06 crashes when opening the parameter dialog of the Fit Panel
with a "buffer overflow detected" message.

Such behavior is caused by calls to strlcpy with an incorrect size of the destination buffer,
which this PR fixes.

Checklist:

• tested changes locally
• updated the docs (if necessary)

[github-actions]

Test Results

    19 files      19 suites   4d 14h 23m 26s ⏱️
 2 665 tests  2 664 ✅ 0 💤 1 ❌
48 742 runs  48 741 ✅ 0 💤 1 ❌

For more details on these failures, see this check.

Results for commit 611fa16.

[bellenot]

LGTM, thanks!