[Crypto] Fix generate_random_bytes for large chunks

Properly handle mbedtls errors, ensure we don't ask more bytes than
allowed for each iteration.

modules/mbedtls/crypto_mbedtls.cpp

@@ -419,9 +419,19 @@ Ref<X509Certificate> CryptoMbedTLS::generate_self_signed_certificate(Ref<CryptoK
 }
 
 PackedByteArray CryptoMbedTLS::generate_random_bytes(int p_bytes) {
+	ERR_FAIL_COND_V(p_bytes < 0, PackedByteArray());
 	PackedByteArray out;
 	out.resize(p_bytes);
-	mbedtls_ctr_drbg_random(&ctr_drbg, out.ptrw(), p_bytes);
+	int left = p_bytes;
+	int pos = 0;
+	// Ensure we generate random in chunks of no more than MBEDTLS_CTR_DRBG_MAX_REQUEST bytes or mbedtls_ctr_drbg_random will fail.
+	while (left > 0) {
+		int to_read = MIN(left, MBEDTLS_CTR_DRBG_MAX_REQUEST);
+		int ret = mbedtls_ctr_drbg_random(&ctr_drbg, out.ptrw() + pos, to_read);
+		ERR_FAIL_COND_V_MSG(ret != 0, PackedByteArray(), vformat("Failed to generate %d random bytes(s). Error: %d.", p_bytes, ret));
+		left -= to_read;
+		pos += to_read;
+	}
 	return out;
 }