STEREO COR2 data are sometimes missing in the app

[AthKouloumvakos]

Sometimes the STEREO COR2 data are missing so the imager is not loaded in the app.

The issue is that the VSO search for STEREO COR2 data does not always return all the availiable Total Brigtnessc (TB) COR2 fits files that are provided by the STEREO site (https://stereo-ssc.nascom.nasa.gov/data/ins_data/secchi/L0/) so the app cannot load this imager because in most of the cases the search returns no TB images for the full date. This issue has been reported to SunPy and it is under ivestigation. More details here: sunpy/sunpy#7439