only display one popup when the player gets to the main hall

[Goober5000]

There are three popups of decreasing priority that can appear in the main hall screen: campaign not found, pilot upgraded, and player tip. Only one of these should actually be displayed -- the first popup will take the player to a different screen, rendering subsequent popups useless; and the second popup is more important than the third popup. This PR prioritizes the popups accordingly.

Yes, this uses goto. It's a succinct and clear way of implementing the necessary logic. It works better than both a one-iteration loop and a cascading if() block.

Fixes #4418.

[jg18]

Instead of goto, how about adding an extra bool flag around line 1061 like

bool popup_shown = false;

then set popup_shown to true on line 1084, and then change lines 1088-1094 to something like this (comments omitted for brevity):

	if (!popup_shown) {
		popup_shown = player_tips_controls();
	}

	if (!popup_shown) {
		player_tips_popup();
	}

Also, to fully appreciate the danger of goto, see https://xkcd.com/292/

[Goober5000]

Yeah, that'll work. It's a sequential if() block, which works better here than a cascading if() block.

My gotos are immune from dinosaur attacks. :P

[jg18]

Thanks, looks good now.