output: when converting OUT_SEGMENT to legacy, don't lose the addend

When converting an OUT_SEGMENT relocation to legacy, the addend is
still significant, as it would represent an explicit addend to the
segment number.

Fixes: https://bugzilla.nasm.us/show_bug.cgi?id=3392783
Reported-by: David Fifield <david@bamsoftware.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Author: H. Peter Anvin

output/legacy.c

@@ -1,6 +1,6 @@
 /* ----------------------------------------------------------------------- *
  *
- *   Copyright 2016-2017 The NASM Authors - All Rights Reserved
+ *   Copyright 2016-2022 The NASM Authors - All Rights Reserved
  *   See the file AUTHORS included with the NASM distribution for
  *   the specific copyright holders.
  *
@@ -89,10 +89,8 @@ void nasm_do_legacy_output(const struct out_data *data)
 
     case OUT_SEGMENT:
         type = OUT_ADDRESS;
-        dptr = zero_buffer;
-        size = (data->flags & OUT_SIGNED) ? -data->size : data->size;
         tsegment |= 1;
-        break;
+        /* fall through */
 
     case OUT_ADDRESS:
         dptr = &data->toffset;