Fix attract title logo slidein (resolves #1273)

- V_SLIDEIN: For (G_IsTitleCardAvailable == false)/(versus at map start == true) contexts, use timeinmap instead of leveltime
- Don't reset timeinmap when reloading gamestate, so it's more functionally equivalent to lt_ticker
These two changes also fix the hypothetical issue of titlecard-less custom gametypes having weird HUD state on late netgame join.

Timeinmap is exclusively used for HUD, as is st_fadein. timeinmap also doesn't increment under g_fastforward, therefore the best candidate to tie together

src/p_setup.cpp

@@ -7645,6 +7645,8 @@ static void P_InitLevelSettings(void)
 
 	// circuit, race and competition stuff
 	numcheatchecks = 0;
+
+	if (!g_reloadinggamestate)
 		timeinmap = 0;
 
 	// special stage

src/st_stuff.c

@@ -1516,10 +1516,10 @@ static fixed_t ST_CalculateFadeIn(player_t *player)
 
 	if (K_CheckBossIntro() == true || G_IsTitleCardAvailable() == false)
 	{
-		if (leveltime <= 16)
+		if (timeinmap <= 16)
 			timer = 0;
 		else
-			timer = leveltime-16;
+			timer = timeinmap-16;
 	}
 
 	if (timer < length)