Bug 66425: Avoid exceptions found via poi-fuzz Prevent a few NullPointerException Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=65450 and https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=63907 and https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=63727