Fixed some dangling listeners in the BLOCKS demos

examples/BLOCKS/BlocksDrawingDemo.h

@@ -313,6 +313,8 @@ public:
        #endif
 
         setSize (600, 600);
+
+        topologyChanged();
     }
 
     ~BlocksDrawingDemo()
@@ -321,6 +323,7 @@ public:
             detachActiveBlock();
 
         lightpadComponent.removeListener (this);
+        topologySource.removeListener (this);
     }
 
     void resized() override

examples/BLOCKS/BlocksMonitorDemo.h

@@ -605,6 +605,13 @@ public:
        #endif
 
         setSize (600, 600);
+
+        topologyChanged();
+    }
+
+    ~BlocksMonitorDemo()
+    {
+        topologySource.removeListener (this);
     }
 
     void paint (Graphics&) override {}

examples/BLOCKS/BlocksSynthDemo.h

@@ -607,12 +607,16 @@ public:
        #endif
 
         setSize (600, 400);
+
+        topologyChanged();
     }
 
     ~BlocksSynthDemo()
     {
         if (activeBlock != nullptr)
             detachActiveBlock();
+
+        topologySource.removeListener (this);
     }
 
     void paint (Graphics& g) override