tls13: read_early_data: set outSz to 0 if no early data

If not data is read, set outSz to 0. This way the
caller can detect if no early data was read.

Author: rizlik

src/tls13.c

@@ -14357,6 +14357,7 @@ int wolfSSL_read_early_data(WOLFSSL* ssl, void* data, int sz, int* outSz)
     if (!IsAtLeastTLSv1_3(ssl->version))
         return BAD_FUNC_ARG;
 
+    *outSz = 0;
 #ifndef NO_WOLFSSL_SERVER
     if (ssl->options.side == WOLFSSL_CLIENT_END)
         return SIDE_ERROR;

tests/api.c

@@ -69268,6 +69268,7 @@ static int test_tls13_early_data(void)
                 ExpectFalse(wolfSSL_is_init_finished(ssl_s));
                 ExpectIntEQ(wolfSSL_read_early_data(ssl_s, msgBuf, sizeof(msgBuf),
                         &read), 0);
+                ExpectIntEQ(read, 0);
                 ExpectTrue(wolfSSL_is_init_finished(ssl_s));
 
                 ExpectIntEQ(wolfSSL_connect(ssl_c), WOLFSSL_SUCCESS);
@@ -69278,7 +69279,7 @@ static int test_tls13_early_data(void)
                 ExpectFalse(wolfSSL_is_init_finished(ssl_s));
                 ExpectIntEQ(wolfSSL_read_early_data(ssl_s, msgBuf, sizeof(msgBuf),
                         &read), 0);
-
+                ExpectIntEQ(read, 0);
                 ExpectTrue(wolfSSL_is_init_finished(ssl_s));
 
                 /* Read server 0.5-RTT data */