GraphEditor: Reduce margin around nodes for backdrop

Author: fabiencastan

meshroom/ui/qml/GraphEditor/GraphEditor.qml

@@ -1358,7 +1358,7 @@ Item {
                     var backdrop
                     if (selectedNodes.length > 0) {
                         // Calculate bounding box of selected nodes
-                        var padding = uigraph.layout.gridSpacing
+                        var padding = uigraph.layout.gridSpacing / 2
                         var minX = Number.MAX_VALUE
                         var minY = Number.MAX_VALUE
                         var maxX = -Number.MAX_VALUE