perf: check if directory in .bazelignore before readdir (#1890)

**What type of PR is this?**
Other

**What package or component does this PR mostly affect?**
all

**What does this PR do? Why is it needed?**

Now that the `.bazelignore` is done before `configure` it can also be
before the `os.ReadDir`.

walk/walk.go

@@ -126,6 +126,10 @@ func Walk(c *config.Config, cexts []config.Configurer, dirs []string, mode Mode,
 }
 
 func visit(c *config.Config, cexts []config.Configurer, isBazelIgnored isIgnoredFunc, knownDirectives map[string]bool, updateRels *UpdateFilter, wf WalkFunc, dir, rel string, updateParent bool) {
+	if isBazelIgnored(rel) {
+		return
+	}
+
 	haveError := false
 
 	// TODO: OPT: ReadDir stats all the files, which is slow. We just care about
@@ -148,10 +152,6 @@ func visit(c *config.Config, cexts []config.Configurer, isBazelIgnored isIgnored
 		haveError = true
 	}
 
-	if isBazelIgnored(rel) {
-		return
-	}
-
 	c = configure(cexts, knownDirectives, c, rel, f)
 	wc := getWalkConfig(c)