When communicating with KMS for CSFLE, the  Crypt.decryptKey wraps bytes read from the KMS TLS stream using:

ByteBuffer.wrap(bytes, 0, bytesRead); 

If InputStream.read(...) on the KMS connection returns -1 (EOF), bytesRead is negative and ByteBuffer.wrap(...) throws IndexOutOfBoundsException with no message. This surfaces to users as:

java.lang.IndexOutOfBoundsException: null
  at java.nio.ByteBuffer.wrap(...)
  at com.mongodb.client.internal.Crypt.decryptKey(...)
...
com.mongodb.MongoClientException: Exception in encryption library: null 

Proposed change

Throw a more informative exception, for example: MongoClientException("Unexpected EOF while communicating with KMS")

Acceptance criteria

• When KMS closes the TLS stream unexpectedly (EOF), the driver no longer throws a bare IndexOutOfBoundsException: null.
• The exception surfaced to the user clearly indicates an unexpected EOF / failure while communicating with KMS.
• Existing successful FLE/KMS behavior is unchanged.