init the spatial last spatial picture if excption
Squashed merge from writenal_refactor2
Merge pull request #325 from sijchen/writenal_refactor3

add encoder error code and refactor WelsWriteNal
remove quality layer configuration. It is not supported
Merge pull request #332 from volvet/remove-q-layer-config

remove quality layer configuration. It is not supported
remove cgs/mgs related code, it is not supported
Remove the WELSAPI definition

There's no need to specify a custom calling convention for
these functions.
Remove the local declarations of the VP interface functions

There's no need to define them manually here, the normal
declarations in IWelsVP.h work just fine even if not loading
the WelsVP library dynamically.
Merge pull request #333 from volvet/remove-mgs-cgs

remove cgs/mgs related code, it is not supported
Merge pull request #322 from volvet/PreProcessExceptionHandle

init the spatial last spatial picture if excption
Merge pull request #334 from mstorsjo/cleanup-vp-interface

Don't use a custom calling convention for the VP library entry points
Merge remote-tracking branch 'upstream/master' into travis.osx