better warnings for invalid width/height args

[Geokureli]

Previously

• if someone passes invalid width/height args into loadGraphic, it may not create any frames, even if the height is off by one and it wont log a warning.
• If they call animation.add with frame indices higher than the sprite's total number of frames, it won't add those frames and it wont log a warning.
• If they call animation.add with no valid frame indices, it won't create the animation, and it won't log a warning.
• If they try to play an animation that doesn't exists it would log: No animation called "$name"

This caused issued where people with incorrect width/height args would get warnings when trying to play anims, and they have no idea why.

Now

• It will log a warning when the desired frameHeight/frameWidth is too big
• It will log a warning when an animation is given an invalid frame
• It will log a warning when they try to make an animation with no valid frames

Example:

import flixel.FlxSprite;
import openfl.display.BitmapData;

class InvalidFrameSizeTestState extends flixel.FlxState
{
	override function create()
	{
		super.create();
		
		final size = 100;
		
		// works fine
		testLoadGraphic(size * 12, size, size, size);
		
		
		/* Warnings:
		 * frameHeight:100 is larger than the graphic's height:99
		 * Could not create animation: a, this sprite has no frames
		 * Could not create animation: b, this sprite has no frames
		 * Could not create animation: c, this sprite has no frames
		 * No animation called "a"
		 * No animation called "b"
		 * No animation called "c"
		 */
		testLoadGraphic(size * 12, size - 1, size, size);
		
		/* Warnings:
		 * Could not add frames above 5 to animation: b
		 * Could not create animation: c, no valid frames were given
		 * No animation called "c"
		 */
		testLoadGraphic(size * 6, size, size, size);
		
	}
	
	function testLoadGraphic(bitmapWidth:Int, bitmapHeight:Int, frameWidth:Int, frameHeight:Int)
	{
		final bmd = new BitmapData(bitmapWidth, bitmapHeight, false);
		final sprite = new FlxSprite();
		sprite.loadGraphic(bmd, true, frameWidth, frameHeight);
		sprite.animation.add("a", [ 0,  1,  2,  3]);
		sprite.animation.add("b", [ 4,  5,  6,  7]);
		sprite.animation.add("c", [ 8,  9, 10, 11]);
		
		sprite.animation.play("a");
		sprite.animation.play("b");
		sprite.animation.play("c");
	}
}