Stop reading EPS image at EOF marker

[radarhere]

Helps #7751

In the issue, there is an EPS file that has other image data after the EOF marker. This additional data causes Pillow to fail to open the file, as one of the lines starts with "%" and is over 255 characters.

This additional image data appears to be a "preview" - in our test images, it is seen in illuCS6_preview.eps, but not illuCS6_no_preview.eps.

Instead, this PR stops reading the data at the EOF marker.