Fix odd-length hex conversion crash

[atirna]

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• I've read the guidelines for contributing to this repository
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Detailed description

rz_hex_str2bin writes one byte for a trailing lone nibble and returns the byte count as a negative value. The old code only reserved hex.length() / 2 bytes, so a single nibble passed an unwritable zero-capacity buffer to Rizin and crashed in rz_hex_str2bin.

I resize the buffer to (length / 2) + 1 before conversion, then use the absolute return value as the final byte count. Odd inputs now keep the padded low nibble without writing past the buffer or passing a negative size to QByteArray::resize.

I used OpenAI Codex (GPT-5.6 Sol) to inspect the affected conversion path and help verify the change.

Test plan (required)

• built the full Cutter target against the bundled Rizin submodule
• before this change, hexStringToBytes("e") crashes with SIGBUS (exit 138)
• after this change, empty input stays empty, 6162 returns 6162, e returns e0, and 61626 returns 616260
• ran xcrun clang-format --dry-run --Werror -style=file src/core/Cutter.cpp

Closing issues

Closes #3641