security: log warning when falling back to weak PRNG

Cryptography: Low

When getrandom() fails, pw_random() silently falls back to rand() or
random_r() seeded from the system clock. This fallback produces
predictable output that should not be used for security-sensitive
operations like WebSocket key generation or network protocol IDs.

Add a warning log message when the fallback is triggered so that
administrators are aware of the degraded random number generation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/pipewire/utils.c

@@ -336,6 +336,7 @@ void pw_random(void *buf, size_t buflen)
 {
 	if (pw_getrandom(buf, buflen, 0) < 0) {
 		uint8_t *p = buf;
+		pw_log_warn("getrandom failed, falling back to weak PRNG");
 		while (buflen-- > 0) {
 			int32_t val;
 #ifdef HAVE_RANDOM_R