target directory setting bug if use ant build environment

report by lgao:

./codegenerator.sh -o ~/jca/generated
if use ant as build envionment

throw exception
   Exception in thread "main" java.lang.NullPointerException
    at org.jboss.jca.codegenerator.Utils.copyFolder(Utils.java:249)
    at org.jboss.jca.codegenerator.Main.copyAllJars(Main.java:728)
    at org.jboss.jca.codegenerator.Main.main(Main.java:134)