common canvas: fix non-updated paints.

When shapes are poped from canvas while retaining shapes instances,
they have no chances to redraw after pushed again due to missing flag.

This patch fixes it by forcely updating flag on pushing time.

@Issues: 181

src/lib/tvgCanvas.cpp

@@ -63,7 +63,7 @@ Result Canvas::draw() noexcept
 
 Result Canvas::update(Paint* paint) noexcept
 {
-    return pImpl->update(paint);
+    return pImpl->update(paint, false);
 }
 
 

src/lib/tvgCanvasImpl.h

@@ -31,7 +31,7 @@
 struct Canvas::Impl
 {
     Array<Paint*> paints;
-    RenderMethod*  renderer;
+    RenderMethod* renderer;
 
     Impl(RenderMethod* pRenderer):renderer(pRenderer)
     {
@@ -49,7 +49,7 @@ struct Canvas::Impl
         if (!p) return Result::MemoryCorruption;
         paints.push(p);
 
-        return update(p);
+        return update(p, true);
     }
 
     Result clear(bool free)
@@ -72,19 +72,20 @@ struct Canvas::Impl
         return Result::Success;
     }
 
-    Result update(Paint* paint)
+    Result update(Paint* paint, bool force)
     {
         if (!renderer) return Result::InsufficientCondition;
 
         Array<RenderData> clips;
+	auto flag = force ? RenderUpdateFlag::All : RenderUpdateFlag::None;
 
         //Update single paint node
         if (paint) {
-            paint->pImpl->update(*renderer, nullptr, 255, clips, RenderUpdateFlag::None);
+            paint->pImpl->update(*renderer, nullptr, 255, clips, flag);
         //Update all retained paint nodes
         } else {
             for (auto paint = paints.data; paint < (paints.data + paints.count); ++paint) {
-                (*paint)->pImpl->update(*renderer, nullptr, 255, clips, RenderUpdateFlag::None);
+                (*paint)->pImpl->update(*renderer, nullptr, 255, clips, flag);
             }
         }
         return Result::Success;

src/lib/tvgPictureImpl.h

@@ -49,13 +49,14 @@ struct Picture::Impl
         if (paint) {
             paint->pImpl->dispose(renderer);
             delete(paint);
-
             return true;
         }
         else if (pixels) {
-            return renderer.dispose(rdata);
+            auto ret =  renderer.dispose(rdata);
+            rdata = nullptr;
+            return ret;
         }
-        return false;
+        return true;
     }
 
     void resize()

src/lib/tvgShapeImpl.h

@@ -215,7 +215,9 @@ struct Shape::Impl
 
     bool dispose(RenderMethod& renderer)
     {
-        return renderer.dispose(rdata);
+        auto ret = renderer.dispose(rdata);
+        rdata = nullptr;
+        return ret;
     }
 
     bool render(RenderMethod& renderer)