No Meaningful Fit Was Possible

Hi,
I'm trying to run the first example on the elliptical isophote fit, replacing the tutorial url of M51 with a FITS cutout from PanStarrs in the i-band. When I run the code line by line, it gets as far as:
`isolist = ellipse.fit_image()`
at which point it tells me no meaningful fit is possible. I have selected the default values such that the guess is right at the center of the galaxy, resized the image, tried different images off of PanStarrs, etc. but I keep getting this error. When the galaxy takes up most of my image, the image is about 150 pixels across.

Here is a reproducible example:

```
from astropy.io import fits
from astropy.utils.data import download_file

url = 'http://ps1images.stsci.edu/cgi-bin/fitscut.cgi?red=/rings.v3.skycell/2594/022/rings.v3.skycell.2594.022.stk.i.unconv.fits&format=fits&x=310.198000&y=72.882500&size=150&wcs=1&imagename=cutout_rings.v3.skycell.2594.022.stk.i.unconv.fits'
path = download_file(url)
hdu = fits.open(path)
data = hdu[0].data
hdu.close()

from photutils.isophote import Ellipse

ellipse = Ellipse(data)

isolist = ellipse.fit_image()
```
This gives this error:

> WARNING: No meaningful fit was possible. [photutils.isophote.ellipse]

Run the reproducible Python example with the supplied PanSTARRS FITS cutout and inspect the call to photutils.isophote.Ellipse.fit_image(). Compare the result with the tutorial's M51 input and determine whether the warning comes from the cutout data or fitting assumptions. Done means the cause is established and the behavior is fixed or clearly documented.

Written by the indexing model from the issue text.