fix: bytestream reads buffered data

[tabcat]

Title

fix: bytestream reads buffered data

Description

bytestream.read checks the bytestream's readBuffer before returning null.
before, bytestream.read would only check if the stream's write side was closed and the stream's write side buffer was empty to return null.

Notes & open questions

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works