Fix undoing Cleanup/Convert to Biblatex
Fix undoing Cleanup/Convert to Biblatex

When Cleanup/Convert to Biblatex converted year/month fields to a date
field, it used to store erroneous undo information. This change fixes
it.

mairdl/jabref,sauliusg/jabref,sauliusg/jabref,tschechlovdev/jabref,tschechlovdev/jabref,oscargus/jabref,Mr-DLib/jabref,jhshinn/jabref,ayanai1/jabref,oscargus/jabref,Mr-DLib/jabref,shitikanth/jabref,Siedlerchr/jabref,tobiasdiez/jabref,mredaelli/jabref,motokito/jabref,JabRef/jabref,grimes2/jabref,ayanai1/jabref,mredaelli/jabref,ayanai1/jabref,mairdl/jabref,jhshinn/jabref,oscargus/jabref,Mr-DLib/jabref,Braunch/jabref,shitikanth/jabref,Siedlerchr/jabref,JabRef/jabref,motokito/jabref,shitikanth/jabref,zellerdev/jabref,bartsch-dev/jabref,oscargus/jabref,sauliusg/jabref,shitikanth/jabref,zellerdev/jabref,Braunch/jabref,Mr-DLib/jabref,obraliar/jabref,tobiasdiez/jabref,oscargus/jabref,ayanai1/jabref,Braunch/jabref,Braunch/jabref,obraliar/jabref,tschechlovdev/jabref,shitikanth/jabref,zellerdev/jabref,jhshinn/jabref,mairdl/jabref,mairdl/jabref,mredaelli/jabref,mredaelli/jabref,Mr-DLib/jabref,Siedlerchr/jabref,bartsch-dev/jabref,mairdl/jabref,Siedlerchr/jabref,JabRef/jabref,obraliar/jabref,grimes2/jabref,tschechlovdev/jabref,zellerdev/jabref,jhshinn/jabref,sauliusg/jabref,grimes2/jabref,obraliar/jabref,zellerdev/jabref,grimes2/jabref,jhshinn/jabref,motokito/jabref,tobiasdiez/jabref,bartsch-dev/jabref,JabRef/jabref,bartsch-dev/jabref,tobiasdiez/jabref,obraliar/jabref,tschechlovdev/jabref,motokito/jabref,Braunch/jabref,mredaelli/jabref,ayanai1/jabref,grimes2/jabref,bartsch-dev/jabref,motokito/jabref