Reset terminate to false during connect()

Fixes bug where you could only open a Shell session on Windows once
per invocation of SyncTERM.

src/syncterm/conn_conpty.c

@@ -216,6 +216,7 @@ int conpty_connect(struct bbslist *bbs)
 	}
 	conn_api.wr_buf_size = BUFFER_SIZE;
 
+	terminate = false;
 	_beginthread(conpty_output_thread, 0, NULL);
 	_beginthread(conpty_input_thread, 0, NULL);