let idp init private key also if the file already exists and is empty

changelog/unreleased/bugfix-idp-init-certificate-empty-file

@@ -0,0 +1,6 @@
+Bugfix: Autocreate IDP private key also if file exists but is empty
+
+We've fixed the behavior for the IDP private key generation so that
+a private key is also generated when the file already exists but is empty.
+
+https://github.com/owncloud/ocis/pull/4394

services/idp/pkg/command/server.go

@@ -161,12 +161,12 @@ func ensureEncryptionSecretExists(path string) error {
 
 func ensureSigningPrivateKeyExists(paths []string) error {
 	for _, path := range paths {
-		_, err := os.Stat(path)
+		file, err := os.Stat(path)
-		if err == nil {
+		if err == nil && file.Size() > 0 {
-			// If the file exists we can just return
+			// If the file exists and is not empty we can just return
 			return nil
 		}
-		if !errors.Is(err, fs.ErrNotExist) {
+		if !errors.Is(err, fs.ErrNotExist) && file.Size() > 0 {
 			return err
 		}