Do not set size unnecessarily if image fails to open

[radarhere]

When opening an image, if the size is missing, EpsImagePlugin sets the image size just before throwing an error.

Pillow/src/PIL/EpsImagePlugin.py

Lines 356 to 359 in 4f7070e

	if not self._size:
	self._size = 1, 1 # errors if this isn't set. why (1,1)?
	msg = "cannot determine EPS bounding box"
	raise OSError(msg)

But if an error is thrown when opening, there is no image afterwards. Consider this example code, derived from the test suite.

import io
from PIL import Image

data = io.BytesIO(b'%!PS-Adobe-3.0 EPSF-3.0\n%%BoundingBox: a b c d\n10 setlinewidth\n10 10 moveto\n0 90 rlineto 90 0 rlineto 0 -90 rlineto closepath\nstroke')
try:
    im = Image.open(data)
except OSError:
    pass
print(im)

gives

Traceback (most recent call last):
  File "demo.py", line 9, in <module>
    print(im)
NameError: name 'im' is not defined

So if there is no image afterwards, why does it need a size? This PR removes the line.