[Media_api] Windows midiOutLongMsg strangeness

[Ben Allison]

Roger,
Did you unprepare (midiOutUnprepareHeader) first?  If the MIDIHDR that was
passed in was already prepared, you'll need to do this.  The MIDIHDR data
structure stores a bool to indicate whether or not it's already been
prepared.  If it's been prepared already, midiOutPrepareHeader exits
immediately without doing anything (or at least the documentation suggests
so).

-Ben Allison

> Ben,
>     That's a good idea, but putting midiOutPrepareHeader() before or
> after the modifications to the MIDIHDR makes no difference, at least in
> my tests. So with midiOutPrepareHeader() in place, sysexs sends to MIDI
> Yoke virtual midi ports only work if I copy the sysex message
> (hdr->lpData) to a freshly allocated block on the heap. Sysex sends to
> my MidiMan 1x1 interface work (at least in my latest tests) using the
> same code but without the memory copy. -Roger
>
>  > When you change where lpData points to, you fiddle with whatever
> "magic"
>  > happens you call midiOutPrepareHeader or midiInPrepareHeader.
>