Fix scrolling when there's no scrollbar.

The code was moving unscrolled lines back after scrolling the
majority of them... if all lines were scrolled, moving some back
actually broke scrolling.

src/conio/bitmap_con.c

@@ -1392,11 +1392,18 @@ bitmap_movetext_screen(int x, int y, int tox, int toy, int direction, int height
 		if (screena.toprow < 0)
 			screena.toprow += screena.screenheight;
 
+		/*
+		 * Set up to move bits that were *not* moved back to
+		 * where they should have stayed.
+		 */
 		if (direction == -1)
 			direction = 1;
 		else
 			direction = -1;
 		height = vstat.rows - height;
+		// If everything was moved, there's no lines to move back
+		if (height <= y - toy)
+			return;
 		int otoy = toy;
 		toy = vstat.rows - (y - toy);
 		y = toy - (y - otoy);