Logger: add extra safety.

Though, that's not really enough for now.

src/Logger/Logger.cpp

@@ -112,6 +112,11 @@ addEntry(EntryType type, StringView message) {
 
 ArrayView<const LogEntry>
 entries() {
+    if(!_logMutex.try_lock()) {
+        return nullptr;
+    }
+    _logMutex.unlock();
+
     return _entries;
 }