Report correct error when FormatMessage fails.

Previously, the original error code would be reported as having come
from FormatMessage.  Spotted by GCC [-Wformat-extra-args].

windows/winmisc.c

@@ -221,7 +221,7 @@ const char *win_strerror(int error)
                            msgtext, lenof(msgtext)-1, NULL)) {
             sprintf(msgtext,
                     "(unable to format: FormatMessage returned %d)",
-                    error, GetLastError());
+                    GetLastError());
         } else {
             int len = strlen(msgtext);
             if (len > 0 && msgtext[len-1] == '\n')