refactoring: check m_debug_… outside of loops
MP4 reader: don't update tables for tracks that aren't requested
fixup! refactoring: check m_debug_… outside of loops
QT/MP4 reader: debug code addition & removal
QT/MP4 reader: don't special-case sample_size == 1 and empty sample_table

Fixes #950.
Merge branch 'fix-mov-pcm-bug-950'

Conflicts:
	ChangeLog