Delay showing editor the window

This fixes Waves V13 VST3 plugins crashing when opening the editor. They
will likely still crash later on anyways because they're kinda broken.
Amazing.

src/wine-host/editor.h

@@ -195,6 +195,13 @@ class Editor {
      */
     void resize(uint16_t width, uint16_t height);
 
+    /**
+     * Show the window, should be called after the plugin has embedded itself.
+     * There's absolutely zero reason why this can't be done in the constructor
+     * or in `do_xembed()`, but it needs to be. Thanks Waves.
+     */
+    void show() noexcept;
+
     /**
      * Handle X11 events sent to the window our editor is embedded in.
      */