G-case compsets with ice-shelf melt fluxes but without data icebergs are broken

[Darin Comeau]

#6229 broke

SMS_D_Ld1.T62_oQU240wLI.GMPAS-IAF-PISMF
SMS_Ld1.T62_oQU240wLI.GMPAS-IAF-DISMF

These compsets do not have DIB, but do have ISMF, and the logic to wrap the new coupling fields did not take this into account.