PR summary

Fix two potential null pointer crashes in src/ft2font.h and src/ft2font_wrapper.cpp.

1. ft_error_string returning NULL (ft2font.h:44)

Fixed by changing the default case to return "unknown error" instead of NULL, so the function always returns a valid string.

2. NULL family_name streamed in ft_glyph_warn (ft2font_wrapper.cpp:408)

Fixed by guarding each stream insertion with (*it ? *it : "unknown").

AI Disclosure

I used Claude Code to help understand the codebase. The fixes were applied by me.

PR checklist

• [N/A] "closes #0000" — no linked issue
• new and changed code is tested
• [N/A] Plotting related features are demonstrated in an example
• [N/A] New Features and API Changes are noted with a directive and release note — these are defensive bug fixes with no API changes
• [N/A] Documentation complies with general and docstring guidelines — no docs changed