1. create new context with smbc_new_context()
2. set auth callback with smbc_setFunctionAuthDataWithContext()
3. call smbc_init_context() on the context
4. NULL is returned and errno is set to EINVAL.

This is due to the following test in libsmb_context.c:

        if (!smbc_getFunctionAuthData(context) ||
            smbc_getDebug(context) < 0 ||
            smbc_getDebug(context) > 100) {
                
                errno = EINVAL;
                return NULL;
                
        }

smbc_getFunctionAuthData() always returns NULL when callback with context is set via smbc_setFunctionAuthDataWithContext(). Modifying the test however causes crash in further code - please check as well.