fix(once-flag): make flag atomic (#6237)

src/util/OnceFlag.cpp

@@ -3,13 +3,12 @@
 namespace chatterino {
 
 OnceFlag::OnceFlag() = default;
-OnceFlag::~OnceFlag() = default;
 
 void OnceFlag::set()
 {
     {
         std::unique_lock guard(this->mutex);
-        this->flag = true;
+        this->flag.store(true, std::memory_order::relaxed);
     }
     this->condvar.notify_all();
 }
@@ -18,7 +17,7 @@ bool OnceFlag::waitFor(std::chrono::milliseconds ms)
 {
     std::unique_lock lock(this->mutex);
     return this->condvar.wait_for(lock, ms, [this] {
-        return this->flag;
+        return this->flag.load(std::memory_order::relaxed);
     });
 }
 
@@ -26,7 +25,7 @@ void OnceFlag::wait()
 {
     std::unique_lock lock(this->mutex);
     this->condvar.wait(lock, [this] {
-        return this->flag;
+        return this->flag.load(std::memory_order::relaxed);
     });
 }