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=2785

Your paranoid android.


=== w864 (32 bit device) ===
device.c:5409: Test failed: pBits not cleared on double lock.
device.c:5410: Test failed: Pitch not cleared on double lock.
device: unhandled exception c0000005 at 742814C8

=== w864 (64 bit device) ===
device.c:5409: Test failed: pBits not cleared on double lock.
device.c:5410: Test failed: Pitch not cleared on double lock.
device: unhandled exception c0000005 at 000007F84EDD90EB