Netty 4 IndexOutOfBoundsException due to writer index exceeding buffer capacity

Netty 4.1.30 and above (plus earlier versions intermittently) fail the following test:

[INFO] Running org.lmdbjava.CursorParamTest
[ERROR] Tests run: 5, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.78 s <<< FAILURE! - in org.lmdbjava.CursorParamTest
[ERROR] execute[4: buffer adapter: org.lmdbjava.CursorParamTest$NettyBufferRunner@68b7bdcb](org.lmdbjava.CursorParamTest)  Time elapsed: 0.015 s  <<< ERROR!
java.lang.IndexOutOfBoundsException: readerIndex: 0, writerIndex: 8 (expected: 0 <= readerIndex <= writerIndex <= capacity(4))
	at io.netty.buffer.AbstractByteBuf.checkIndexBounds(AbstractByteBuf.java:112)
	at io.netty.buffer.AbstractByteBuf.readerIndex(AbstractByteBuf.java:121)
	at org.lmdbjava.ByteBufProxy.out(ByteBufProxy.java:144)
	at org.lmdbjava.ByteBufProxy.out(ByteBufProxy.java:39)
	at org.lmdbjava.KeyVal.valOut(KeyVal.java:133)
	at org.lmdbjava.Cursor.get(Cursor.java:153)
	at org.lmdbjava.CursorParamTest$AbstractBufferRunner.execute(CursorParamTest.java:127)
	at org.lmdbjava.CursorParamTest.execute(CursorParamTest.java:90)

Two issues were identified in ButeBufProxy:

The unsafe setting of the LENGTH_OFFSET was setting the value as a long, whereas the actual field in the Java PooledByteBuf type is an int.
The order of updating the readerIndex before the writerIndex was causing the bounds check on the readerIndex call to fail as the writerIndex had not yet been corrected.

Correction of the above causes tests to pass consistently with Netty 4.1.32 (currently the latest version).

cc #90 #96 #111