Call VVV_exit() when SDL_QUIT is received

This fixes a regression introduced by #535 where a quit signal (e.g.
Ctrl-C) sent to the window while the game was in unfocus pause wouldn't
close the game.

One problem was that key.quitProgram would only be checked when control
flow switched back to the outer loop in main(), which would only happen
when the loop order state machine switched to a delta function. As the
unfocused func table didn't have any delta functions, this means
key.quitProgram would never be checked.

So a naïve solution to this would just be to add a no-op delta func
entry to the unfocused func table. However, we then run into a separate
issue where a delta function at the end of a func list never reassigns
the active funcs, causing the game to be stuck in the unfocus pause
forever. Active func reassignment only happens after fixed funcs. So
then a naïve solution after that would be to simply add a no-op fixed
func entry after that. And indeed, that would fix the whole issue.

However, I want to do things the right way. And this does not seem like
the right way. Even putting aside the separate last-func-being-delta
issue, it mandates that every func list needs a delta function. Which
seems quite unnecessary to me.

Another solution I considered was copy-pasting the key.quitProgram check
to the inner loops, or adding some sort of signal propagation to
the inner loops - implemented by copy-pasting checks after each loop -
so we didn't need to copy-paste key.quitProgram... but that seems really
messy, too.

So, I realized that we could throw away key.quitProgram, and simply call
VVV_exit() directly when we receive an SDL_QUIT event. This fixes the
issue, this removes an unnecessary middleman variable, and it's pretty
cleanly and simply the right thing to do.

desktop_version/src/KeyPoll.cpp

@@ -5,6 +5,7 @@
 #include <string.h>
 #include <utf8/unchecked.h>
 
+#include "Exit.h"
 #include "Game.h"
 #include "Graphics.h"
 #include "Music.h"
@@ -36,7 +37,6 @@ KeyPoll::KeyPoll(void)
 	// 0..5
 	sensitivity = 2;
 
-	quitProgram = 0;
 	keybuffer="";
 	leftbutton=0; rightbutton=0; middlebutton=0;
 	mx=0; my=0;
@@ -339,7 +339,7 @@ void KeyPoll::Poll(void)
 
 		/* Quit Event */
 		case SDL_QUIT:
-			quitProgram = true;
+			VVV_exit(0);
 			break;
 		}
 	}

desktop_version/src/KeyPoll.h

@@ -37,7 +37,6 @@ public:
 
 	bool resetWindow;
 
-	bool quitProgram;
 	void toggleFullscreen(void);
 
 	int sensitivity;

desktop_version/src/main.cpp

@@ -615,7 +615,7 @@ int main(int argc, char *argv[])
     gamestate_funcs = get_gamestate_funcs(game.gamestate, &num_gamestate_funcs);
     loop_assign_active_funcs();
 
-    while(!key.quitProgram)
+    while (true)
     {
         f_time = SDL_GetTicks();