Change the buffer boundary check and alert type

Signed-off-by: XiaokangQian <xiaokang.qian@arm.com>
diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index 68f5ae5..2c2d0f3 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -1510,11 +1510,11 @@
     }
 
     /* Check that we consumed all the message. */
-    if( p != extensions_end )
+    if( p != end )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "EncryptedExtension lengths misaligned" ) );
-        MBEDTLS_SSL_PEND_FATAL_ALERT( MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER,   \
-                                      MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER );
+        MBEDTLS_SSL_PEND_FATAL_ALERT( MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR,   \
+                                      MBEDTLS_ERR_SSL_DECODE_ERROR );
         return( MBEDTLS_ERR_SSL_DECODE_ERROR );
     }