[ui] MediaLibrary: enable dynamicRoles on mediaModel

If an outside 3D media file is the first thing ever loaded, 'model.attribute' will be initialized to 'null' and will prevent an actual Attribute to be associated to this role. This breaks media loading from within Meshroom.

Author: yann-lty

meshroom/ui/qml/Viewer3D/MediaLibrary.qml

@@ -30,7 +30,7 @@ Entity {
 
     QtObject {
         id: m
-        property ListModel mediaModel: ListModel {}
+        property ListModel mediaModel: ListModel { dynamicRoles: true }
         property var sourceToEntity: ({})
 
         readonly property var mediaElement: ({