Fix null termination of CLAP metadata strings

[Stormrage-DJ]

Replaces three bounded strncpy calls with snprintf in the JUCE CLAP wrapper.

When an input string fills the destination buffer exactly, strncpy may omit
the terminating NUL byte. The replacement preserves bounded truncation while
guaranteeing a valid C string for CLAP hosts.

Validation:

• Applied cleanly to current main
• Strict Windows CLAP build completed successfully

[baconpaul]

Thanks!