don't fail if no folder found with Groovy tests

Files:
copied: from /trunk/webtest/releasetests/tests/build.xml (r45206) to /trunk/webtest/releasetests/build.xml (try)
deleted: /trunk/webtest/releasetests/tests/build.xml
modified: /trunk/webtest/webtest.xml (try)
modified: /trunk/webtest/releasetests/tests/TestSuite.xml (try)