Linux: Fix bad window error when using the XEmbedComponent

The issue was reproducible by opening a plugin window in the AudioPluginHost.

modules/juce_audio_processors/format_types/juce_LV2PluginFormat.cpp

@@ -3190,6 +3190,7 @@ private:
             Inner() : XEmbedComponent (true, true)
             {
                 setOpaque (true);
+                setVisible (true);
                 addToDesktop (0);
             }
         };