[Bug] IsoTest underflows

[GregHib]

IsoTest algorithm doesn't round correctly
https://i.imgur.com/s009X0U.png

libgdxplayground/core/src/io/piotrjastrzebski/playground/isotiled/IsoTest.java

Lines 61 to 62 in 0c88b72

	int x = (int)((isoPos.y)/2f - .5f);
	int y = (int)((isoPos.x)/2f + .5f);

Values should be Math.floored (alternatively checked if positive)