fix: do not split near empty ranges

[mutianf]

Catch the exception

Completed work item 4231779587829057376 UNSUCCESSFULLY: UNKNOWN: java.lang.IllegalStateException: Refusing to interpolate for near-empty ByteKeyRange{startKey=[6c617267652d6b6579], endKey=[6c617267652d6b657900]} where start and end keys differ only by trailing zero bytes.
	at org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkState(Preconditions.java:601)
	at org.apache.beam.sdk.io.range.ByteKeyRange.interpolateKey(ByteKeyRange.java:238)
	at com.google.cloud.bigtable.beam.CloudBigtableIO$Reader.splitAtFraction(CloudBigtableIO.java:838)