Aside from being the right place, we depend on schan_get_buffer() not
returning a buffer if there's no space left in schan_imp_recv() /
schan_imp_send().

This uses a new, Wine-specific registry key
<HKCU\Software\Wine\Drivers\wine<driver>.drv> to determine the correct
device to use for the various defaults. The drivers still supply their
own defaults which will be chosen if no registry entry is defined. For
portability we use a driver-specific key in order to support default
devices for each of the driver backends.

Also localize the error dialog while we're in there.