[applets/batterymonitor] Don't show percentage overlay with no batteries

There's no point, since it always says "-" and just covers up the icon.
Let's only show the overlay if there are actually any batteries.

BUG: 435890
FIXED-IN: 5.22

applets/batterymonitor/package/contents/ui/CompactRepresentation.qml

@@ -86,9 +86,9 @@ MouseArea {
                     anchors.bottom: parent.bottom
                     anchors.right: parent.right
 
-                    visible: plasmoid.configuration.showPercentage
+                    visible: plasmoid.configuration.showPercentage && batteryContainer.hasBattery
 
-                    text: batteryContainer.hasBattery ? i18nc("battery percentage below battery icon", "%1%", percent) : i18nc("short symbol to signal there is no battery currently available", "-")
+                    text: i18nc("battery percentage below battery icon", "%1%", percent)
                     icon: batteryIcon
                 }
             }