HOPKINS: Fix Sprite_Vesa() height clipping

This fixes some Valgrind warnings on the city overhead map, and also
seem to get rid of the bird "droppings" previously left behind in the
area beneath the picture. There are things I don't understand about
this function, but I hope I didn't break anything.

engines/hopkins/graphics.cpp

@@ -952,6 +952,7 @@ void GraphicsManager::Sprite_Vesa(byte *surface, const byte *spriteData, int xp,
 	}
 
 	// Clip Y
+	clip_y1 = height;
 	if (yp <= 0)
 		return;
 	if (yp < _minY + 300) {
@@ -999,7 +1000,7 @@ void GraphicsManager::Sprite_Vesa(byte *surface, const byte *spriteData, int xp,
 	// Handling for clipped versus non-clipped
 	if (_clipFl) {
 		// Clipped version
-		for (int yc = 0; yc < height; ++yc, destP += _lineNbr2) {
+		for (int yc = 0; yc < clip_y1; ++yc, destP += _lineNbr2) {
 			byte *tempDestP = destP;
 			byte byteVal;
 			int xc = 0;