ipcache: Error out from InjectLabels if Checker is nil

K8s cache is not fully synced also when k8sSyncedChecker is still nil.

Found during code inspection, not sure if this can manifest as a bug on
runtime.

Fixes: #17823
Signed-off-by: Jarno Rajahalme <jarno@isovalent.com>

pkg/ipcache/metadata.go

@@ -109,8 +109,7 @@ func (ipc *IPCache) InjectLabels(src source.Source) error {
 		return ErrLocalIdentityAllocatorUninitialized
 	}
 
-	if ipc.k8sSyncedChecker != nil &&
-		!ipc.k8sSyncedChecker.K8sCacheIsSynced() {
+	if ipc.k8sSyncedChecker == nil || !ipc.k8sSyncedChecker.K8sCacheIsSynced() {
 		return errors.New("k8s cache not fully synced")
 	}