azureblob: retry InvalidBlobOrBlock error as it may indicate block concurrency problems

According to Microsoft support this error can be caused by

> A timing/concurrency issue where the PUT operations are happening
> about the same time for a single blob. The Put Block List operation
> writes a blob by specifying the list of block IDs that make up the
> blob. In order to be written as part of a blob, a block must have
> been successfully written to the server in a prior Put Block
> operation.
>
> Documentation reference:
>
> https://docs.microsoft.com/en-us/rest/api/storageservices/put-block
>
> This error can happen when doing concurrent upload commits after you
> have started the upload but before you commit. In that case, the
> upload fails. The application can retry this error or attempt some
> other recovery action based on the required scenario.

See: https://forum.rclone.org/t/error-while-syncing-with-azure-blob-storage-x-ms-error-code-invalidbloborblock/15561

backend/azureblob/azureblob.go

@@ -257,6 +257,12 @@ var retryErrorCodes = []int{
 func (f *Fs) shouldRetry(err error) (bool, error) {
 	// FIXME interpret special errors - more to do here
 	if storageErr, ok := err.(azblob.StorageError); ok {
+		switch storageErr.ServiceCode() {
+		case "InvalidBlobOrBlock":
+			// These errors happen sometimes in multipart uploads
+			// because of block concurrency issues
+			return true, err
+		}
 		statusCode := storageErr.Response().StatusCode
 		for _, e := range retryErrorCodes {
 			if statusCode == e {
@@ -1322,7 +1328,7 @@ outer:
 			// Upload the block, with MD5 for check
 			md5sum := md5.Sum(buf)
 			transactionalMD5 := md5sum[:]
-			err = o.fs.pacer.Call(func() (bool, error) {
+			err := o.fs.pacer.Call(func() (bool, error) {
 				bufferReader := bytes.NewReader(buf)
 				wrappedReader := wrap(bufferReader)
 				rs := readSeeker{wrappedReader, bufferReader}