[ui] ImageGallery: display the correct image in the Viewer after a re…

…moval

When an image is removed from the gallery, the adjacent one is
automatically selected in the GridView. However, as the index in the
GridView would not change (the adjacent image taking the place of the
removed one), the 2D viewer would not receive any update and no more image
would be displayed. Even if the index in the GridView remains the same,
the 2D viewer now is updated with the newly selected image.

meshroom/ui/qml/ImageGallery/ImageGallery.qml

@@ -42,8 +42,9 @@ Panel {
 
         onViewpointsChanged: {
             // The model has been updated, but the GridView is yet to be filled with the new data: reset the grid index
-            if (grid.count == 0 && grid.count != viewpoints.count)
+            if (grid.count == 0 && grid.count != viewpoints.count) {
                 grid.currentIndex = -1;
+            }
         }
     }
 
@@ -168,10 +169,14 @@ Panel {
             }
 
             onCountChanged: {
-                /* If the grid index is -1, then it has been reset when the model was updated and the grid emptied
-                   Set it to 0 to select the first element now that it is filled */
                 if (grid.currentIndex == -1 && grid.count > 0) {
+                    /* If the grid index is -1, then it has been reset when the model was updated and the grid emptied
+                       Set it to 0 to select the first element now that it is filled */
                     grid.currentIndex = 0
+                } else {
+                    /* The count is updated but the current index is valid: an image has been added or removed. The
+                       index remains unchanged, but the selected image has changed. */
+                    grid.currentIndexChanged()
                 }
             }