add optional dictionary convenience function

MVMCore/MVMCore/Categories/Dictionary+MFConvenience.swift

@@ -193,3 +193,13 @@ public extension Dictionary {
         return previousObject
     }
 }
+
+public extension Optional where Wrapped == Dictionary<AnyHashable, Any> {
+    
+    func dictionaryAdding(key: AnyHashable, value: Any) -> Dictionary<AnyHashable, Any> {
+        var dictionary = self ?? [:]
+        dictionary[key] = value
+        return dictionary
+    }
+    
+}