MT#55283 further compiler warning fixes

for #1690

Follow up to 37d7762f

Change-Id: Id58204db5a733b3d821cbef855fac72451484b41

daemon/sdp.c

@@ -3307,9 +3307,8 @@ int sdp_create(str *out, struct call_monologue *monologue, struct sdp_ng_flags *
 		print_sdp_media_section(s, media, NULL, flags, rtp_ps_link, true, false);
 	}
 
-	out->s = s->str;
 	out->len = s->len;
-	g_string_free(s, FALSE);
+	out->s = g_string_free(s, FALSE);
 	return 0;
 err:
 	if (s)

lib/str.h

@@ -320,9 +320,8 @@ INLINE str *g_string_free_str(GString *gs) {
 	assert(gs->len >= pl);
 	assert(memcmp(gs->str, STR_MALLOC_PADDING, pl) == 0);
 	ret = (void *) gs->str;
-	ret->s = gs->str + pl;
 	ret->len = gs->len - pl;
-	g_string_free(gs, FALSE);
+	ret->s = g_string_free(gs, FALSE) + pl;
 	return ret;
 }
 INLINE int str_memcmp(const str *s, void *m) {