🔧 Fix memory leak in pthread init functions on failure

🔧 Fix memory leak in pthread init functions on failure

When pthread_mutex_init() or pthread_cond_init() fails in the debug
implementation (DEBUGLEVEL >= 1), the previously allocated memory was
not freed, causing a memory leak.

This fix ensures that allocated memory is properly freed when pthread
initialization functions fail, preventing resource leaks in error
conditions.

The issue affects:
- ZSTD_pthread_mutex_init() at lib/common/threading.c:146
- ZSTD_pthread_cond_init() at lib/common/threading.c:167

This is particularly important for long-running applications or
scenarios with resource constraints where pthread initialization
might fail due to system limits.