fromByteBuffer() not working properly in Int32Serializer/IntegerSerializer

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Hello,

It seems to me fromByteBuffer() should work with bytebuffers with more bytes remaining too, as it is only reading the next 4 bytes.

Also, the instance field in Int32Serializer was not initialized correctly.

Thanks.

Olivier

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This makes fromByteBuffer() of Int32Serializer/IntegerSerializer more coherent with BooleanSerializer behaviour.

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Actually, I added a small fix for LongSerializer too.