Avoid potential UB in loggers using composition

This cast would work fine, but any other fields added to those loggers
would be left uninitialized.

src/common/logging/vst3.h

@@ -19,9 +19,25 @@
 #include "common.h"
 
 /**
- * Provides VST3-specific logging functionality for debugging plugins.
+ * Wraps around `Logger` to provide VST3 specific logging functionality for
+ * debugging plugins. This way we can have all the complex initialisation be
+ * performed in one place.
  */
-class Vst3Logger : public Logger {
+class Vst3Logger {
    public:
+    Vst3Logger(Logger& generic_logger);
+
+    /**
+     * @see Logger::log
+     */
+    inline void log(const std::string& message) { logger.log(message); }
+
+    /**
+     * @see Logger::log_trace
+     */
+    inline void log_trace(const std::string& message) { logger.log(message); }
+
     // TODO: Logging interface for VST3 plugins
+
+    Logger& logger;
 };