Do not register existing extensions

Author: adazem009

src/scratchconfiguration_p.cpp

@@ -1,13 +1,17 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #include <scratchcpp/iextension.h>
+#include <algorithm>
 
 #include "scratchconfiguration_p.h"
 
 using namespace libscratchcpp;
 
 void ScratchConfigurationPrivate::registerExtension(std::shared_ptr<IExtension> extension)
 {
+    if (std::find(extensions.begin(), extensions.end(), extension) != extensions.cend())
+        return;
+
     extensions.push_back(extension);
 }