Only read a stream as far as required by the analyzers. An EndStreamAnalyzer is assumed to do so already. ThroughStreamAnalyzers now have a function bool isReadyWithStream() that can be called to check if the stream has to be read any further. StreamIndexer takes advantage of this new function to reduce the reading it does.

This optimisation has no real effect unless streams that are required to read the entire stream (e.g. DigestStreamAnalyzer) can be turned off.
This possibility will be added later.