Adjust caption pop-in by tics instead of frames

Fixes STJr/SRB2#900 pop-in animation being affected by framerate

src/screen.c

@@ -621,7 +621,13 @@ void SCR_ClosedCaptions(void)
 		y = basey-((i + 2)*10);
 
 		if (closedcaptions[i].b)
-			y -= (closedcaptions[i].b--)*vid.dupy;
+		{
+			y -= closedcaptions[i].b * vid.dupy;
+			if (renderisnewtic)
+			{
+				closedcaptions[i].b--;
+			}
+		}
 
 		if (closedcaptions[i].t < CAPTIONFADETICS)
 			flags |= (((CAPTIONFADETICS-closedcaptions[i].t)/2)*V_10TRANS);