This was suggested by wm4 and stefano.
After this patch using align=1 the size used by various functions would not
contain padding, while the palette would be aligned at align>1

This patch makes it required to use align>=4 if the palette is to be accessed
as uint32

As a side-effect It fixes storing pal8 in nut with odd with&height
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>