concentrate calculation of minimal loaded UID in load_box()

so it's in one place with the maximal one, sans the one-sided
preparation of the bulk range + exception list.

src/sync.c

@@ -808,8 +808,7 @@ box_opened2( sync_vars_t *svars, int t )
 	svars->opts[N] = svars->drv[N]->prepare_load_box( ctx[N], opts[N] );
 
 	ARRAY_INIT( &mexcs );
-	if (svars->opts[F] & OPEN_OLD) {
+	if ((svars->opts[F] & OPEN_OLD) && chan->max_messages) {
-		if (chan->max_messages) {
 		/* When messages have been expired on the near side, the far side fetch is split into
 		 * two ranges: The bulk fetch which corresponds with the most recent messages, and an
 		 * exception list of messages which would have been expired if they weren't important. */
@@ -835,13 +834,10 @@ box_opened2( sync_vars_t *svars, int t )
 	} else {
 		minwuid = 1;
 	}
-	} else {
-		minwuid = UINT_MAX;
-	}
 	sync_ref( svars );
 	load_box( svars, F, minwuid, mexcs.array );
 	if (!check_cancel( svars ))
-		load_box( svars, N, (svars->opts[N] & OPEN_OLD) ? 1 : UINT_MAX, (uint_array_t){ NULL, 0 } );
+		load_box( svars, N, 1, (uint_array_t){ NULL, 0 } );
 	sync_deref( svars );
 }
 
@@ -863,13 +859,15 @@ load_box( sync_vars_t *svars, int t, uint minwuid, uint_array_t mexcs )
 	uint maxwuid = 0, pairuid = UINT_MAX;
 
 	if (svars->opts[t] & OPEN_NEW) {
-		if (minwuid > svars->maxuid[t] + 1)
+		if (!(svars->opts[t] & OPEN_OLD) || (minwuid > svars->maxuid[t] + 1))
 			minwuid = svars->maxuid[t] + 1;
 		maxwuid = UINT_MAX;
 		if (svars->opts[t] & OPEN_OLD_IDS)  // Implies OPEN_OLD
 			pairuid = get_seenuid( svars, t );
 	} else if (svars->opts[t] & OPEN_OLD) {
 		maxwuid = get_seenuid( svars, t );
+	} else {
+		minwuid = UINT_MAX;
 	}
 	info( "Loading %s box...\n", str_fn[t] );
 	svars->drv[t]->load_box( svars->ctx[t], minwuid, maxwuid, svars->finduid[t], pairuid, svars->maxuid[t], mexcs, box_loaded, AUX );