[ui] ImageGallery: update the Viewer2D correctly when the GridView's …

…item changes

This commit ensures that any change in the ImageGallery's GridView
selection is correctly reflected in the Viewer2D. In particular:
- When a new project file is opened, the first image in the gallery
is now displayed in the 2D viewer, after a correct auto-fit has been
applied
- When an image in the gallery is removed, the adjacent image that
becomes selected is automatically displayed in the 2D viewer

meshroom/ui/qml/ImageGallery/ImageGallery.qml

@@ -173,7 +173,9 @@ Panel {
             Connections {
                 target: _reconstruction
                 onSelectedViewIdChanged: {
-                    grid.updateCurrentIndexFromSelectionViewId()
+                    if (_reconstruction.selectedViewId > -1) {
+                        grid.updateCurrentIndexFromSelectionViewId()
+                    }
                 }
             }
             function makeCurrentItemVisible()
@@ -183,12 +185,12 @@ Panel {
             function updateCurrentIndexFromSelectionViewId()
             {
                 var idx = grid.model.find(_reconstruction.selectedViewId, "viewId")
-                if(idx >= 0 && grid.currentIndex != idx) {
+                if (idx >= 0 && grid.currentIndex != idx) {
                     grid.currentIndex = idx
                 }
             }
-            onCurrentIndexChanged: {
-                if(grid.updateSelectedViewFromGrid) {
+            onCurrentItemChanged: {
+                if (grid.updateSelectedViewFromGrid && grid.currentItem) {
                     _reconstruction.selectedViewId = grid.currentItem.viewpoint.get("viewId").value
                 }
             }