Handle pending data in TLS buffers

There might be more bytes left in the current TLS record, even if
there is nothing on the underlying stream. Make sure we properly
return this when we aren't being requested to block.

common/rdr/TLSInStream.cxx

@@ -111,9 +111,11 @@ size_t TLSInStream::readTLS(U8* buf, size_t len, bool wait)
 {
   int n;
 
-  n = in->check(1, 1, wait);
-  if (n == 0)
-    return 0;
+  if (gnutls_record_check_pending(session) == 0) {
+    n = in->check(1, 1, wait);
+    if (n == 0)
+      return 0;
+  }
 
   n = gnutls_record_recv(session, (void *) buf, len);
   if (n == GNUTLS_E_INTERRUPTED || n == GNUTLS_E_AGAIN)