BinaryDictionary may fail reading a file [LUCENE-5855]

The following code may fail on other JVMs, e.g. on Android:

final ByteBuffer tmpBuffer = ByteBuffer.allocateDirect(size);
final ReadableByteChannel channel = Channels.newChannel(dictIS);
final int read = channel.read(tmpBuffer);
if (read != size) {
throw new EOFException("Cannot read whole dictionary");
}

The code expects that channel.read() will fill entire buffer contents, which is however not the case: ReadableByteChannel.read() may even decide to read 0 bytes and this mimicks InputStream.read() behavior. The current Lucene code accidentally works on Oracle Java because Oracle Java channel.read() fills the buffer fully (just check the Channels.newChannel() implementation).

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Migrated from [LUCENE-5855](https://issues.apache.org/jira/browse/LUCENE-5855) by Martin Vysny

Start by locating the BinaryDictionary code described in the issue and read the surrounding channel and ByteBuffer handling. Check the ReadableByteChannel.read() contract across JVM implementations, including Android. Done means dictionary files are read reliably when a channel returns fewer bytes than requested, with the existing EOF behavior preserved.

Written by the indexing model from the issue text.