Jan Schmidt authored Apr 08, 2020 and Tim-Philipp Müller committed Jan 13, 2021

Even when pulling a new 64KB buffer from upstream, don't return
more data than was asked for in the pull_range() method and then
return less later, as that confused subclasses like h264parse.

Add a unit test that when a subclass asks for more data, it always
receives a larger buffer on the next iteration, never less.

Fixes #530

Part-of: <!733>