Add thread safety to ContinuationProcess.Add

See #2

Author: muckSponge

UnityAsync/Assets/UnityAsync/Manager/AsyncManager.ContinuationProcessorGroup.ContinuationProcessor.cs

@@ -57,6 +57,16 @@ public void Process()
 
 				[MethodImpl(MethodImplOptions.AggressiveInlining)]
 				public void Add(in T cont)
+				{
+					if(InUnityContext)
+						AddFast(cont);
+					else
+						AddThreadSafe(cont);
+				}
+
+				// only call in UnitySynchronizationContext - not thread safe
+				[MethodImpl(MethodImplOptions.AggressiveInlining)]
+				void AddFast(in T cont)
 				{
 					try
 					{
@@ -86,6 +96,15 @@ public void Add(in T cont)
 					}
 				}
 
+				// use when you may be adding an awaiter from outside of UnitySynchronizationContext
+				[MethodImpl(MethodImplOptions.AggressiveInlining)]
+				async void AddThreadSafe(T cont)
+				{
+					await UnitySyncContext;
+
+					AddFast(cont);
+				}
+
 				[MethodImpl(MethodImplOptions.AggressiveInlining)]
 				static void AssertQueueSize(int queueSize)
 				{