Fix failing PLC build when building freshly created project that use default libraries blocks. When controller loads libraries according to attibutes in project files (BeremizRoot/Enable_{libname}_Library), use known default if attribute is missing.

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<?xml version='1.0' encoding='utf-8'?>

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<BeremizRoot URI_location="LOCAL://">

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  <TargetType/>

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  <Libraries Enable_Python_Library="true"/>

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</BeremizRoot>