fix NullPointerException for path.list() at v0.9.19

java.lang.NullPointerException
    at me.piebridge.bible.Bible.checkZipData(Bible.java:889)
    at me.piebridge.bible.Bible.access$100(Bible.java:45)
    at me.piebridge.bible.Bible$1.run(Bible.java:875)
    at java.lang.Thread.run(Thread.java:856)