Fixed PHOTCORR returning InternalError when phot value is zero, which must be allowed for SBC blocking filters.
Fixed PHOTCORR returning InternalError when phot value is zero, which must be allowed for SBC blocking filters.

git-svn-id: cc674101e2b794ddc2100b657215d55256e3fd48@27231 fe389314-cf27-0410-b35b-8c050e845b92

jhunkeler/hstcal,jhunkeler/hstcal,jhunkeler/hstcal