[skottie] Treat color properties as optional (default black)

TBR=
Change-Id: I51029b5718ec9925c214709ae4e3497dae130d37
Reviewed-on: https://skia-review.googlesource.com/141544
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
diff --git a/modules/skottie/src/Skottie.cpp b/modules/skottie/src/Skottie.cpp
index 20390ee..760d9c5 100644
--- a/modules/skottie/src/Skottie.cpp
+++ b/modules/skottie/src/Skottie.cpp
@@ -254,12 +254,12 @@
 
 sk_sp<sksg::Color> AttachColor(const skjson::ObjectValue& jcolor, AttachContext* ctx) {
     auto color_node = sksg::Color::Make(SK_ColorBLACK);
-    auto color_attached = BindProperty<VectorValue>(jcolor["c"], &ctx->fAnimators,
+    BindProperty<VectorValue>(jcolor["c"], &ctx->fAnimators,
         [color_node](const VectorValue& c) {
             color_node->setColor(ValueTraits<VectorValue>::As<SkColor>(c));
         });
 
-    return color_attached ? color_node : nullptr;
+    return color_node;
 }
 
 sk_sp<sksg::Gradient> AttachGradient(const skjson::ObjectValue& jgrad, AttachContext* ctx) {