Reduce layout shift when loading mutual rooms in user profiles

Instead of making the visibility of this section in user profiles
dependent on the model, its now checking if you can check mutual rooms
and using a busy indicator. There's also a label for when you have no
rooms in common, which is a rare case (for example, banned or left
users.)

src/app/qml/UserDetailDialog.qml

@@ -401,18 +401,36 @@ Kirigami.Dialog {
         Kirigami.Heading {
             text: i18nc("@title The set of common rooms between your current user and the one shown", "Mutual Rooms")
             level: 4
-            visible: !root.isSelf && root.hasMutualRooms
+            visible: !root.isSelf && root.connection.canCheckMutualRooms
 
             Layout.topMargin: Kirigami.Units.largeSpacing
         }
 
         RowLayout {
             spacing: Kirigami.Units.smallSpacing
-            visible: !root.isSelf && root.hasMutualRooms
+            visible: !root.isSelf && root.connection.canCheckMutualRooms
 
             Layout.topMargin: Kirigami.Units.smallSpacing
 
+            QQC2.BusyIndicator {
+                visible: roomRepeater.count === 0 && root.model.loading
+
+                Layout.preferredWidth: Kirigami.Units.iconSizes.medium
+                Layout.preferredHeight: Kirigami.Units.iconSizes.medium
+            }
+
+            QQC2.Label {
+                visible: roomRepeater.count === 0 && !root.model.loading
+                text: i18nc("@info:label", "No rooms in common")
+                verticalAlignment: Text.AlignVCenter
+
+                Layout.preferredHeight: Kirigami.Units.iconSizes.medium
+                Layout.fillHeight: true
+            }
+
             Repeater {
+                id: roomRepeater
+
                 model: root.limiterModel
 
                 delegate: KirigamiComponents.AvatarButton {