A DVD menu is now defined as any time a NAV packet defines at least one button.  This should allow more flexibility to skip some intros.

Refs #11292
Quieten debug output when a DVD still frame is active
Apply timestretch setting to DVD stills.

Refs #11292
Merge remote-tracking branch 'upstream/master'
Initialize member variables in ctor

In patch 4dc18c79d3d3b1885b251318f404473c5e691c2a
member variables were initialized in mythsystemunix.cpp
to fix a coverity issue.  Do the same in
mythsystemwindows.cpp for consistency (and because
if static analysis was run on the windows source,
it would likely report the same issue).

Signed-off-by: Gary Buhrmaster <gary.buhrmaster@gmail.com>