tls-socket: Handle sending fatal errors better

In particular as server, the previous code might cause it to hang in
recv() if this case wasn't triggered by a close notify (followed by a
shutdown of the socket) but it e.g. failed processing a ServerHello and
responded with a fatal alert.

Fixes: 09fbaad6bd ("tls-socket: Don't fail reading if sending data failed")

src/libtls/tls_socket.c

@@ -193,11 +193,13 @@ static bool exchange(private_tls_socket_t *this, bool wr, bool block)
 				case SUCCESS:
 					return TRUE;
 				default:
-					if (wr)
+					if (!wr && this->app.in_done > 0)
-					{
+					{	/* return data after proper termination via fatal close
-						return FALSE;
+						 * notify to which we responded with one */
+						this->eof = TRUE;
+						return TRUE;
 					}
-					break;
+					return FALSE;
 			}
 			break;
 		}