terminal: Set blank cursor on keyboard press

This way we can better see the contents of the terminal.  Show cursor again
on pointer motion.
diff --git a/clients/terminal.c b/clients/terminal.c
index 7b2ce21..ec0f1de 100644
--- a/clients/terminal.c
+++ b/clients/terminal.c
@@ -2137,6 +2137,8 @@
 	    handle_bound_key(terminal, input, sym, time))
 		return;
 
+	input_set_pointer_image(input, CURSOR_BLANK);
+
 	switch (sym) {
 	case XKB_KEY_F11:
 		if (state == WL_KEYBOARD_KEY_STATE_RELEASED)