Fix potential issue in GUI thread mutual recursion

While the assumption that this is always the last element should hold
true, there may be exceptions so better be safe than sorry.

src/wine-host/bridges/vst3.h

@@ -273,7 +273,9 @@ class Vst3Bridge : public HostBridge {
             // once we receive a response
             std::lock_guard lock(mutual_recursion_contexts_mutex);
             current_io_context->stop();
-            mutual_recursion_contexts.pop_back();
+            mutual_recursion_contexts.erase(
+                std::find(mutual_recursion_contexts.begin(),
+                          mutual_recursion_contexts.end(), current_io_context));
 
             response_promise.set_value(response);
         });