vector/helper: let VGradientCache has perfect singletone interface.

diff --git a/src/vector/vdrawhelper.cpp b/src/vector/vdrawhelper.cpp
index d6fa3d1..e3ae7a8 100644 (file)
--- a/src/vector/vdrawhelper.cpp
+++ b/src/vector/vdrawhelper.cpp
@@ -135,6 +135,9 @@ protected:
         return cache_entry;
     }
 
+private:
+    VGradientCache() = default;
+
     VGradientColorTableHash mCache;
     std::mutex              mMutex;
 };