(l2gi_prev): Don't read memory before the start of an array.

src/server/local-to-global.c

@@ -1368,6 +1368,8 @@ l2gi_next(L2g_iterator *l2gi)
     const struct l2g_block_info *binfo;
     int                arrindex;
 
+    assert(!l2gi->search_ended);
+
     l2g      = l2gi->l2g;
     arrindex = l2gi->arrindex + 1;
     for (binfo = l2gi->binfo;
@@ -1457,11 +1459,12 @@ l2gi_prev(L2g_reverse_iterator *l2gi)
     const struct l2g_block_info *binfo;
     int                arrindex;
 
+    assert(!l2gi->search_ended);
+
     l2g      = l2gi->l2g;
     arrindex = l2gi->arrindex - 1;
-    for (binfo = l2gi->binfo;
-	 binfo >= l2g->blocks;
-	 --binfo, arrindex = binfo->first_free - 1)
+    binfo = l2gi->binfo;
+    while (1)
     {
 	for (; arrindex >= 0; --arrindex)
 	{
@@ -1482,10 +1485,16 @@ l2gi_prev(L2g_reverse_iterator *l2gi)
 		return;
 	    }
 	}
-    }
 
-    l2gi->search_ended = 1;
-    return;
+	if (binfo == l2g->blocks)
+	{
+	    l2gi->search_ended = 1;
+	    return;
+	}
+	
+	--binfo;
+	arrindex = binfo->first_free - 1;
+    }
 }