qmp: fix thread termination issue

- the qmp reader_thread should be joined at qmp destructor
or terminate called without an active exception error will happen.

Signed-off-by: Mahmoud Kamel <quic_mkamel@quicinc.com>

qemu-components/qmp/include/qmp.h

@@ -143,6 +143,13 @@ class qmp : public sc_core::sc_module
             }
         }
     }
+
+    ~qmp()
+    {
+        if (reader_thread.joinable()) {
+            reader_thread.join();
+        }
+    }
 };
 
 extern "C" void module_register();