swscale: Use alpha from the right row in yuva2rgba_c

Every other pixel had the alpha channel taken from the wrong
row.

This fixes bug 504.

CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>
Merge remote-tracking branch 'qatar/master'

* qatar/master:
  swscale: Use alpha from the right row in yuva2rgba_c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Fix vdpau vc1 interlace modes also when using decoder vc1_vdpau.

Signed-off-by: Carl Eugen Hoyos <cehoyos@ag.or.at>
vc1dec: Call ff_vdpau_vc1_decode_picture() once for each field.

Fixes mplayer -vc ffvc1vdpau for interlaced streams.
Cosmetics: Fix indentation and add braces after last commit.