Fix byte-safe memo truncation edge case in Stellar memo handling

[Biokes]

Summary

Fixes a narrow edge case in truncateMemoToStellarLimit where a memo could still receive a spurious Unicode replacement character (�) after truncation.

Previously, the safety check for a broken UTF-8 boundary was gated on whether the original input already contained a replacement character. That meant a memo that legitimately contained � before the truncation cut point could bypass the guard, and in a rare case the truncated byte tail could still re-encode to the same byte length while injecting an extra replacement character.

This patch removes that extra condition and relies only on the byte round-trip-length check to detect a broken truncation boundary.

File changed

• frontend/src/components/support-panel.tsx

What changed

• Updated truncateMemoToStellarLimit so it detects invalid truncation boundaries based solely on whether the decoded output still round-trips to the same byte length.
• Removed the original guard that checked !input.includes("�").
• Keeps the existing byte-safe truncation behavior for multibyte UTF-8 characters and prevents accidental injection of replacement characters in the memo.

Closes #1238
Closes #1239
Closes #1240
Closes #1241

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