OpenGEX: fix some review findings.

code/OpenGEXExporter.cpp

@@ -50,6 +50,10 @@ OpenGEXExporter::OpenGEXExporter() {
 OpenGEXExporter::~OpenGEXExporter() {
 }
 
+bool OpenGEXExporter::exportScene( const char *filename, const aiScene* pScene ) {
+    return true;
+}
+
 #endif // ASSIMP_BUILD_NO_OPENGEX_EXPORTER
 
 } // Namespace OpenGEX