[PATCH] wincodecs: Trigger conversion to target format in WriteSource()

[Vincent Povirk]

> Despite the removing a questionable FIXME this part of the code won't do
> what you think it does.

I think it will request a specific pixel format, and the encoder may
actually set a different format if it does not support that one. Am I
missing something?

> Besides, since there is no a single todo_wine
> removed with this patch adding a bunch of tests for different encoders
> is needed to show that the automatic conversion is really supposed to
> happen, and that it doesn't depend on the implementation detail in some
> of the encoders. According to my testing not every encoder does this
> kind of thing, especially when a conversion needs a palette.

As long as some of them do, it makes sense to have it in common code,
and if we need to refine the behavior for individual encoders we can
do that later.