#668 SoapUI is not able load old plugins

[hedon]

SoapUI is not able load plugin implemented old way. In log could not be found any detailed message. Message is only:

[DefaultSoapUICore] Could not load plugin from file [/path/to/soapui/plugins/test-plugin.jar]

Error seems to be in class DefaultSoapUICore#loadOldStylePluginFrom when try to add items from plugin to repository cause an
exception (which is sank in DefaultSoapUICore#loadPlugins method).

Access to repositories should be through proper getter where registry is initialized when is null.

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Tested on version 5.1.2.