Corrected Palm P mode save

[radarhere]

Removes an xfail

Pillow/Tests/test_file_palm.py

Lines 58 to 59 in 8878511

	@pytest.mark.xfail(reason="Palm P image is wrong")
	def test_p_mode(tmp_path: Path) -> None:

with the following changes

1. Always save the colormap for a P mode image, because
   

   Pillow/src/PIL/PalmImagePlugin.py

   Lines 118 to 120 in 8878511

   	if im.mode == "P":
   	# we assume this is a color Palm image with the standard colormap,
   	# unless the "info" dict has a "custom-colormap" field

   
   is an odd assumption.
2. Use OR instead of AND to apply the custom colormap flag
   

   Pillow/src/PIL/PalmImagePlugin.py

   Line 177 in 8878511

   flags = flags & _FLAGS["custom-colormap"]

3. Do not presume that palettes are 256 in length.

At first glance, you might think that

Pillow/src/PIL/PalmImagePlugin.py

Lines 209 to 214 in 8878511

	elif colormapmode == "RGBA":
	fp.write(
	o8(colormap[4 * i])
	+ o8(colormap[4 * i + 1])
	+ o8(colormap[4 * i + 2])
	)

offered support for saving RGBA palettes. But if you look again, you will see that is only writing three values, meaning it's not writing RGBA palettes, it's converting them to RGB. However, getpalette() will only return a RGB palette, so we won't need to worry about handling that.