wined3d: Initialize map_desc in wined3d_surface_map

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://newtestbot.winehq.org/JobDetails.pl?Key=2784

Your paranoid android.


=== w864 (32 bit device) ===
device.c:2481: Test failed: Expected foreground window 000401A6, got 00010084.
device.c:3174: Test failed: Expected wndproc 0x4107a0, got 0x4107a0.
device: unhandled exception c0000005 at 742F14C8