Because 4a8e8bb1bd changed the
NVENCAPI_STRUCT_VERSION define to rely on enc->needs_compat_ver, we must
do the conditional check and define needs_compat_ver before any structs
are initialized because they will check the version when doing so by
calling NVENCAPI_STRUCT_VERSION internally.
In this case, make sure that we define enc->needs_compat_ver before
NV_ENCODE_API_FUNCTION_LIST_VER is called for
NV_ENCODE_API_FUNCTION_LIST.
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