refactor(tvix/nar-bridge): Clean up directory popping loop

This change got lost in the rebases in cl/9348. There's unnecessary
`break`/`continues` that can be replaced by moving the conditional into
the for loop condition.

Change-Id: I559e21087630b05e483f768ab59f8067961a2eae
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9352
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/nar-bridge/pkg/reader/reader.go

@@ -195,16 +195,11 @@ func (r *Reader) Import(
 
 			// We don't need to worry about the root node case, because we can only finish the root "/"
 			// If we're at the end of the NAR reader (covered by the EOF check)
-			for {
-				// We never want to pop the root directory until we're completely done.
-				if len(stack) > 1 && !strings.HasPrefix(hdr.Path, stack[len(stack)-1].path+"/") {
+			for len(stack) > 1 && !strings.HasPrefix(hdr.Path, stack[len(stack)-1].path+"/") {
 				err := popFromStack()
 				if err != nil {
 					return nil, fmt.Errorf("unable to pop from stack: %w", err)
 				}
-					continue
-				}
-				break
 			}
 
 			if hdr.Type == nar.TypeSymlink {