fix crash when non selecting

NppChnConvPlugin/PluginBridge.cs

@@ -50,6 +50,7 @@ namespace NppChnConvPlugin
             {
                 var start = CurrentEditor.GetSelectionNStart(i);
                 var end = CurrentEditor.GetSelectionNEnd(i);
+                if (end.Value - start.Value < 1) continue;
 
                 CurrentEditor.SetTargetStart(start);
                 CurrentEditor.SetTargetEnd(end);