Fix regression crash with post-only detours #3

If there were no pre-detour handlers registered for a detour, there was no return Action of the pre hook available in a post hook, so don't try to access it.

DynamicHooks/hook.cpp

@@ -156,8 +156,12 @@ ReturnAction_t CHook::HookHandler(HookType_t eHookType)
 {
 	if (eHookType == HOOKTYPE_POST)
 	{
-		ReturnAction_t lastPreReturnAction = m_LastPreReturnAction.back();
-		m_LastPreReturnAction.pop();
+		ReturnAction_t lastPreReturnAction = ReturnAction_Ignored;
+		// Ignore hooks without a registered pre-hook handler.
+		if (!m_LastPreReturnAction.empty()) {
+			lastPreReturnAction = m_LastPreReturnAction.back();
+			m_LastPreReturnAction.pop();
+		}
 		if (lastPreReturnAction == ReturnAction_Override)
 			m_pCallingConvention->RestoreReturnValue(m_pRegisters);
 		if (lastPreReturnAction < ReturnAction_Supercede)