Use GetDefaultParams instead of memset to initialize SEncParamExt in the console test app

Most of the default parameters still are overwritten with hardcoded
values in FillSpecificParameters though, but this makes sure that
defaults are applied for any new fields at least.
Only force iLoopFilterDisableIdc to 2 if multithreading has been enabled

Previously these lines were within an #ifdef MT_ENABLED block,
but now that threading is enabled by default, we should probably
only do it if threading has been requested.
refactor code to eliminate potential div by 0
Merge pull request #1061 from mstorsjo/welsenc-init-defaults

Use GetDefaultParams instead of memset to initialize SEncParamExt in the console test app
Merge pull request #1076 from lyao2/RCdiv

refactor code to eliminate potential div by 0, review at: https://rbcommons.com/s/OpenH264/r/595/
Merge pull request #1060 from mstorsjo/loopfilter-multithreading

Only force iLoopFilterDisableIdc to 2 if multithreading has been enabled
Merge remote-tracking branch 'upstream/master' into travis.osx