coredata: Handle AttributeError in unpickling coredata
coredata: Handle AttributeError in unpickling coredata

Which can happen due to internal refactorings, such as the removal of
the ConfData class between 0.49 and 0.50

mesonbuild/meson,jpakkane/meson,pexip/meson,jpakkane/meson,jpakkane/meson,pexip/meson,jpakkane/meson,becm/meson,QuLogic/meson,pexip/meson,mesonbuild/meson,pexip/meson,QuLogic/meson,becm/meson,QuLogic/meson,QuLogic/meson,mesonbuild/meson,pexip/meson,becm/meson,QuLogic/meson,jpakkane/meson,mesonbuild/meson,mesonbuild/meson,QuLogic/meson,jpakkane/meson,mesonbuild/meson,becm/meson,jpakkane/meson,mesonbuild/meson,mesonbuild/meson,becm/meson,becm/meson,mesonbuild/meson,jpakkane/meson,becm/meson,pexip/meson,pexip/meson,pexip/meson,jpakkane/meson,becm/meson,QuLogic/meson,pexip/meson,mesonbuild/meson,QuLogic/meson,pexip/meson,becm/meson,QuLogic/meson,becm/meson