Open 1 bit EPS in mode 1

[radarhere]

Resolves #6382

When reading an encoded bitmap image in an EPS image, Pillow uses the information contained within the comment to set the image mode.

Pillow/src/PIL/EpsImagePlugin.py

Lines 288 to 296 in 92b0f2c

	# Encoded bitmapped image.
	x, y, bi, mo = s[11:].split(None, 7)[:4]
	if int(bi) != 8:
	break
	try:
	self.mode = self.mode_map[int(mo)]
	except ValueError:
	break

Unless the bitmap depth is not 8, then it doesn't. This PR sets the mode to 1 if the bitmap depth is 1.

For more information about the comment structure, see http://paulbourke.net/dataformats/psdpsb/psdpsb.html#50577413_61897

The test image image comes from the issue.