Force minimum value of desiredBundleSizeBytes to be 1

Fixes apache#28793 in the way suggested in apache#28793 (comment):

- `BoundedReadEvaluatorFactory#getInitialInputs` may still calculate a
  `bytesPerBundle` of `0`; but
- `BigtableSource#split` will interpret it as `1` in order to not
  violate the `checkArgument()` in
  https://github.com/apache/beam/blob/71c8459633ec86e576eca080a26be9f42474ecb2/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigtable/BigtableIO.java#L1623-L1626

CHANGES.md

@@ -86,6 +86,7 @@
 * Fixed exception chaining issue in GCS connector (Python) ([#26769](https://github.com/apache/beam/issues/26769#issuecomment-1700422615)).
 * Fixed streaming inserts exception handling, GoogleAPICallErrors are now retried according to retry strategy and routed to failed rows where appropriate rather than causing a pipeline error (Python) ([#21080](https://github.com/apache/beam/issues/21080)).
 * Fixed a bug in Python SDK's cross-language Bigtable sink that mishandled records that don't have an explicit timestamp set: [#28632](https://github.com/apache/beam/issues/28632).
+* Fixed "Desired bundle size 0 bytes must be greater than 0" in BigtableSource when you have more cores than bytes to read [#28793](https://github.com/apache/beam/issues/28793).
 
 
 ## Security Fixes

sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigtable/BigtableIO.java

@@ -1326,7 +1326,11 @@ public List<BigtableSource> split(long desiredBundleSizeBytes, PipelineOptions o
       long maximumNumberOfSplits = 4000;
       long sizeEstimate = getEstimatedSizeBytes(options);
       desiredBundleSizeBytes =
-          Math.max(sizeEstimate / maximumNumberOfSplits, desiredBundleSizeBytes);
+          Math.max(
+              sizeEstimate / maximumNumberOfSplits,
+              // BoundedReadEvaluatorFactory may provide us with a desiredBundleSizeBytes of 0
+              // https://github.com/apache/beam/issues/28793
+              Math.max(1, desiredBundleSizeBytes));
 
       // Delegate to testable helper.
       List<BigtableSource> splits =