fix decrement handling

repertory/librepertory/src/file_manager/ring_buffer_base.cpp

@@ -327,13 +327,15 @@ void ring_buffer_base::reader_thread(bool is_forward) {
       if (next_chunk > ring_end_) {
         next_chunk = ring_pos_;
       }
-    } else if (last_marker != ring_begin_) {
-      last_marker = ring_begin_;
-      next_chunk = ring_pos_;
-    }
+    } else {
+      if (last_marker != ring_begin_) {
+        last_marker = ring_begin_;
+        next_chunk = ring_pos_;
+      }
 
-    if (next_chunk > ring_begin_) {
-      --next_chunk;
+      if (next_chunk > ring_begin_) {
+        --next_chunk;
+      }
     }
 
     if (read_state_[next_chunk % read_state_.size()]) {