Check_MK Werk 5260: Fix presentation of mirrored areas

ID: 5260 Title: Fix presentation of mirrored areas Component: metrics Level: 1 Class: Bug fix Version: 1.5.0i1 This werk fixes a bug in Check_MK metrics system: When chosing "Mirrored Area" as a style in Graph Designer for multiple metrics, a "Mirrored Stacked" presentation got displayed instead.