Fix initialization of  mri.chart[:data][:groups]
Fix initialization of  mri.chart[:data][:groups]

Thanks to nil format variable initialization code
was not reached in build_document_header.
(transferred from ManageIQ/manageiq@bd40cc504e4e8c13f4ca20e286997ddd8343a436)

ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic