Merge pull request #60962 from technicianted/flex_race_fix

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Added missing error check that could cause kubelet to crash

**What this PR does / why we need it**:
Adds missing error check. An error can happen due to a race condition when watched files change, or become inaccessible. This can happen if a file was added to the driver directory then quickly removed, in which case the callback will be called with non-nil `err` and nil `info`, which is not checked, causing kubelet to crash.

**Which issue(s) this PR fixes**:
Fixes #60861

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```

pkg/volume/flexvolume/probe.go

@@ -176,7 +176,7 @@ func (prober *flexVolumeProber) updateProbeNeeded() {
 // on its parent directory.
 func (prober *flexVolumeProber) addWatchRecursive(filename string) error {
 	addWatch := func(path string, info os.FileInfo, err error) error {
-		if info.IsDir() {
+		if err == nil && info.IsDir() {
 			if err := prober.watcher.AddWatch(path); err != nil {
 				glog.Errorf("Error recursively adding watch: %v", err)
 			}