Bug 460

Steps to Reproduce:

1. Give the item of size -5, 2 along with the arrival and the departure dates.
2. Give the slot size of 7.

Throwing an exception i.e Array Index Out of Bounds for findOnePerfectFit in the optimize method!

Also need to throw an error for the negative value of an item.

Given test case:

@Test
	void testOptimize12()
	{
		Slot ss = new Slot(7);
		Item is1 = new Item(-5, new Day("13-Oct-2020"),new Day("20-Oct-2020"));
		Item is2 = new Item(2, new Day("13-Oct-2020"),new Day("20-Oct-2020"));
		ArrayList<Item> itemArray = new ArrayList<Item>();
		itemArray.add(is1);
		itemArray.add(is2);
		Optimize op = new Optimize();
		op.findOnePerfectSubsets(itemArray, itemArray.size(), 3, ss);
		assertEquals(true, op.getFound());
	}