core/log: add a mutex to protect stdoutStream

QTextStream is not thread safe.

src/core/logging.cpp

@@ -14,6 +14,7 @@
 #include <qlist.h>
 #include <qlogging.h>
 #include <qloggingcategory.h>
+#include <qmutex.h>
 #include <qnamespace.h>
 #include <qobject.h>
 #include <qobjectdefs.h>
@@ -220,6 +221,7 @@ void LogManager::messageHandler(
 	}
 
 	if (display) {
+		auto locker = QMutexLocker(&self->stdoutMutex);
 		LogMessage::formatMessage(
 		    self->stdoutStream,
 		    message,

src/core/logging.hpp

@@ -10,6 +10,7 @@
 #include <qlatin1stringview.h>
 #include <qlogging.h>
 #include <qloggingcategory.h>
+#include <qmutex.h>
 #include <qobject.h>
 #include <qtmetamacros.h>
 
@@ -135,6 +136,7 @@ private:
 	QHash<QLatin1StringView, CategoryFilter> allFilters;
 
 	QTextStream stdoutStream;
+	QMutex stdoutMutex;
 	LoggingThreadProxy threadProxy;
 
 	friend void initLogCategoryLevel(const char* name, QtMsgType defaultLevel);