winmm: fix WOD_Open() WAVE_MAPPER no-device case.

[Andrew Eikum]

On Tue, Aug 20, 2013 at 05:57:34AM +0200, Fabrice Bauzac wrote:
> Hello,
> 
> This patch intends to fix the bug:
> http://bugs.winehq.org/show_bug.cgi?id=34305
> 
> The bug: basically, when there is no sound device and the user tries
> to WOD_Open() the WAVE_MAPPER pseudodevice, the code calls read_map()
> with device index 0 without first checking whether the number of
> devices is greater than 0.
> 

Looks good to me, thanks. I tested on Windows 7, and the error code is
correct.

By the way, the waveIn path (WID_Open) has the same bug. Feel free to
fix that, too, if you want. Or I'll submit a patch myself later.

Andrew