DAP: Fix MSVC warning

conversion from 'size_t' to 'int', possible loss of data

Change-Id: Iaea0dde9be1bec467dd788058dc7b64c7af33da4
Reviewed-by: Artem Sokolovskii <artem.sokolovskii@qt.io>

src/plugins/debugger/dap/dapengine.h

@@ -35,7 +35,7 @@ public:
     void handleNext();
 
     VariableItem currentItem() const { return m_currentVarItem; }
-    int queueSize() const { return m_queue.size(); }
+    int queueSize() const { return int(m_queue.size()); }
 
 private:
     void startHandling();