fellow_cache: fellow_busy_obj_trim_seglists and off==0

src/fellow_cache.c

@@ -5209,6 +5209,9 @@ fellow_busy_obj_trim_seglists(struct fellow_busy *fbo)
 	fcsl->next = NULL;
 	fdsl = fcsl->fdsl;
 	fellow_busy_region_free(fbo, &fdsl->next);
+	// we do not use -1 consistently for "unset offset"
+	if (fdsl->next.off == -1)
+		fdsl->next.off = 0;
 	AZ(fdsl->next.off);
 	AZ(fdsl->next.size);