This filter reads entire structs at a time from the SvStream, including
structs that are derived from other structs.  This happens to work fine
with GCC by chance, but MSVC AMD64 by default aligns structs to 8 bytes,
and that means if sizeof(super-stuct) = 20 then 4 bytes of padding are
inserted and that ruins the import.

This causes vcl_filters_test to go into an infinite loop reading
SaveAsPicture.sgv.

Fix this by reading each member of the structs separately, which also
means that the filter doesn't need to byte-swap every member on
big-endian platforms since SvStream methods already do that.

Change-Id: I237725dbcde5232006728179e645776fcb79cac3