PROTON-215: Fix bug in JNI array decoding discovered by new tests.

getJavaArray() was getting the array type from the first call to next(), which
fails if the array is empty. Fix is to use getArrayType() to get the type.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1449944 13f79535-47bb-0310-9956-ffa450edef68