Fix leak of heap-allocated mutexes

rtengine/rtlensfun.h

@@ -57,7 +57,7 @@ private:
     lfModifier *data_;
     bool swap_xy_;
     int flags_;
-    MyMutex *lfModifierMutex;
+    mutable MyMutex lfModifierMutex;
 };
 
 class LFCamera final
@@ -122,7 +122,7 @@ private:
     LFDatabase();
     bool LoadDirectory(const char *dirname);
 
-    MyMutex *lfDBMutex;
+    mutable MyMutex lfDBMutex;
     static LFDatabase instance_;
     lfDatabase *data_;
 };