Fix raster mask

[Twice22]

When creating a PSD file from numpy arrays. According to the documentation we should use the -2 index to precise the user_mask (a.k.a the raster mask in Photoshop).
For example. Let's say I want to create a RGB image with Alpha channel fully opaque and with a gradient on the raster mask. Here is what I will do:

        channels = {}
	channels[-2] = (255 * np.tile(np.linspace(0, 1, 600), [500, 1])).astype(np.uint8)  # Raster mask
	channels[-1] = 255 * np.ones((500, 600), dtype=np.uint8)  # Alpha
	channels[0] = np.zeros((500, 600), dtype=np.uint8)  # Red
	channels[1] = 255 * np.ones((500, 600), dtype=np.uint8)  # Green
	channels[2] = np.zeros((500, 600), dtype=np.uint8)  # Blue

	over = nested_layers.Image(
	        name="overlay_image", visible=True, opacity=255, group_id=0,
	        blend_mode=enums.BlendMode.normal, top=0, left=0, channels=channels,
	        metadata=None, layer_color=0, color_mode=3)

For example let's create a group containing 2 layers:

• bottom layer: Red layer
• upper layer: Green layer with gradient on the raster mask

	from pytoshop.user import nested_layers
	from pytoshop import enums
	import numpy as np

	# channels for the bottom layer (RGBA) with full red and alpha fully opaque
	channels = {
		0: 255 * np.ones((500, 600), dtype=np.uint8),
		1: np.zeros((500, 600), dtype=np.uint8),
		2: np.zeros((500, 600), dtype=np.uint8),
		-1: 255 * np.ones((500, 600), dtype=np.uint8)
	}

        # color_mode=3 specifies RGB color
	base = nested_layers.Image(
		name="base_image", visible=True, opacity=255, group_id=0,
		blend_mode=enums.BlendMode.normal, top=0, left=0, channels=channels,
		metadata=None, layer_color=0, color_mode=3)


        # upper layer with RGBA + gradient on the raster mask
        channels = {}
	channels[-2] = (255 * np.tile(np.linspace(0, 1, 600), [500, 1])).astype(np.uint8)  # Raster mask
	channels[-1] = 255 * np.ones((500, 600), dtype=np.uint8)  # Alpha
	channels[0] = np.ones((500, 600), dtype=np.uint8)  # Red
	channels[1] = 255 * np.ones((500, 600), dtype=np.uint8)  # Green
	channels[2] = np.ones((500, 600), dtype=np.uint8)  # Blue

	over = nested_layers.Image(
		name="overlay_image", visible=True, opacity=255, group_id=0,
		blend_mode=enums.BlendMode.normal, top=0, left=0, channels=channels,
		metadata=None, layer_color=0, color_mode=3)

        # group the `base` and the `over` layers
	group = nested_layers.Group(
		name="overlay", visible=True, opacity=255,
		group_id=0, blend_mode=enums.BlendMode.normal, layers=[over, base], closed=True,
		metadata=None, layer_color=0
	)

	with open('my_output.psd', 'wb') as fd:
		output = nested_layers.nested_layers_to_psd([group], color_mode=3)
		output.write(fd)

This, will, unfortunately not work with the current version of pytoshop as the mask of the layer containing the raster mask will have bottom=0 and right=0. To fix this issue we need to precise both the right and the bottom when creating the LayerMask from the LayerRecord object instance.

This Pull Request fix this issue!