[Bug 51265] New: valgrind shows an uninitialized read in is_wow64_thread()

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=51265

Bug ID: 51265
           Summary: valgrind shows an uninitialized read in
                    is_wow64_thread()
           Product: Wine
           Version: 6.9
          Hardware: x86-64
                OS: Linux
            Status: NEW
          Keywords: valgrind
          Severity: normal
          Priority: P2
         Component: wineserver
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

==875840== Conditional jump or move depends on uninitialised value(s)
==875840==    at 0x1493A6: is_wow64_thread (registry.c:2074)
==875840==    by 0x1493A6: req_create_key (???:0)
==875840==    by 0x14AAC2: call_req_handler (request.c:312)
==875840==    by 0x14B9E7: read_request (request.c:367)
==875840==    by 0x15350F: thread_poll_event (thread.c:383)
==875840==    by 0x128D45: fd_poll_event (fd.c:525)
==875840==    by 0x128D45: main_loop_epoll (???:0)
==875840==    by 0x128FAD: main_loop (fd.c:985)
==875840==    by 0x11AA61: main (main.c:149)

The problem is that a process that's starting up makes a couple of
create_key/open_key calls before it maps the main image.

This can be trivially fixed by initializing the "machine" field. None of the
keys we open are actually sensitive to architecture (well, one is, but we use
the WOW64_64KEY flag on it). Still, it strikes me as a little fragile. Can we
determine the architecture any earlier?