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.
Merge pull request #1061 from mstorsjo/welsenc-init-defaults

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