Always use resizable buffers

It was a slight problem for audio buffers, but events can apparently
also have an arbitrary size because of chunks.

src/wine-host/plugin-bridge.h

@@ -115,5 +115,5 @@ class PluginBridge {
      * A scratch buffer for sending and receiving data during `process` and
      * `processReplacing` calls.
      */
-    std::unique_ptr<AudioBuffers::buffer_type> process_buffer;
+    std::vector<uint8_t> process_buffer;
 };