Explicitly list opcodes that should return strings

The automatic detection works fine in every case I've tested other than
Fabfilter plugins, but this is probably for the best.

src/wine-host/plugin-bridge.cpp

@@ -352,6 +352,13 @@ class HostCallbackDataConverter : DefaultDataConverter {
                 // done inside of `passthrough_event`.
                 return AEffect(*plugin);
                 break;
+            // We detect whether an opcode should return a string by checking
+            // whether there's a zeroed out buffer behind the void pointer. This
+            // works for any host, but not all plugins zero out their buffers.
+            case audioMasterGetVendorString:
+            case audioMasterGetProductString:
+                return WantsString{};
+                break;
             default:
                 return DefaultDataConverter::read(opcode, index, value, data);
                 break;