Cleanup: move variable assignment out of the loop

It never changes inside this function, so there's no need to recompute
it with every loop iteration.

Equivalent to the change that was made to isDescendentOfSelectedNodes in
files_controller.go in d0c6e27fee.

pkg/gui/controllers/commits_files_controller.go

@@ -642,9 +642,10 @@ func normalisedSelectedCommitFileNodes(selectedNodes []*filetree.CommitFileNode)
 }
 
 func isDescendentOfSelectedCommitFileNodes(node *filetree.CommitFileNode, selectedNodes []*filetree.CommitFileNode) bool {
+	nodePath := node.GetPath()
+
 	for _, selectedNode := range selectedNodes {
 		selectedNodePath := selectedNode.GetPath()
-		nodePath := node.GetPath()
 
 		if strings.HasPrefix(nodePath, selectedNodePath) && nodePath != selectedNodePath {
 			return true