[qt6][Viewer] Viewer2D: Fix fit() with the Sequence Player

With the Sequence Player always enabled by default, the `fit()` function
must be triggered at the right moment, and only once the layout has
been correctly initialized; otherwise, zoom factors may become negative
and the images will not be placed correctly in the viewer.

Changes in the orientation tag must be handled independently from the
state of the zoom factor.

Author: cbentejac

meshroom/ui/qml/Viewer/Viewer2D.qml

@@ -501,9 +501,9 @@ FocusScope {
                         var sizeValid = (width > 0) && (height > 0)
                         var layoutValid = (root.width > 50) && (root.height > 50)
                         var sizeChanged = (root.previousWidth != width) || (root.previousHeight != height)
-                        
+
                         if ((!root.fittedOnce && imgContainer.image && sizeValid && layoutValid) ||
-                            (root.fittedOnce && sizeChanged && sizeValid && layoutValid)) {                            
+                            (root.fittedOnce && sizeChanged && sizeValid && layoutValid)) {
                             var ret = fit()
                             if (!ret)
                                 return
@@ -515,12 +515,16 @@ FocusScope {
                         }
                     }
 
-                    onHeightChanged : {
+                    onWidthChanged : {
                         floatImageViewerLoader.sizeChanged();
                     }
 
                     Connections {
                         target: root
+                        function onWidthChanged() {
+                            floatImageViewerLoader.sizeChanged()
+                        }
+
                         function onHeightChanged() {
                             floatImageViewerLoader.sizeChanged()
                         }
@@ -534,7 +538,6 @@ FocusScope {
                             var ret = fit()
                             if (!ret)
                                 return
-                            root.fittedOnce = true
                             root.previousWidth = width
                             root.previousHeight = height
                             root.previousOrientationTag = orientationTag