qga: fix off-by-one length check

Laszlo Ersek said: "The length check is off by one (in the safe direction); it
should be (nchars >= 2). The processing should be active for the wide string
L"\r\n" -- resulting in the empty wide string --, I believe."

Reported-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qga/commands-win32.c

@@ -1323,7 +1323,7 @@ get_net_error_message(gint error)
     if (msg != NULL) {
         nchars = wcslen(msg);
 
-        if (nchars > 2 &&
+        if (nchars >= 2 &&
             msg[nchars - 1] == L'\n' &&
             msg[nchars - 2] == L'\r') {
             msg[nchars - 2] = L'\0';