Default constructor for AutoCF

making this more like our rcp<>

Diffs=
7e1393ae7 Default constructor for AutoCF

.rive_head

diff --git a/.rive_head b/.rive_head
index 837e8db..d4c9491 100644
--- a/.rive_head
+++ b/.rive_head
@@ -1 +1 @@
-788d6675c7bb03731023b29a3a7f61deb96fb35e
+7e1393ae7bda97daf4bd481756d24b94696722e4

skia/renderer/include/mac_utils.hpp

diff --git a/skia/renderer/include/mac_utils.hpp b/skia/renderer/include/mac_utils.hpp
index 8c4a6f5..139a1ba 100644
--- a/skia/renderer/include/mac_utils.hpp
+++ b/skia/renderer/include/mac_utils.hpp
@@ -57,7 +57,7 @@
     T m_Obj;
 
 public:
-    AutoCF(T obj) : m_Obj(obj) {}
+    AutoCF(T obj = nullptr) : m_Obj(obj) {}
     ~AutoCF() {
         if (m_Obj)
             CFRelease(m_Obj);