Test: Backport EdDSA junit changes from github; fixes NPE in 2 tests

core/java/build.xml

...java/test/junit/net/i2p/crypto/eddsa/EdDSAEngineTest.java

...t/net/i2p/crypto/eddsa/math/AbstractFieldElementTest.java

...a/test/junit/net/i2p/crypto/eddsa/math/ConstantsTest.java

...est/junit/net/i2p/crypto/eddsa/math/GroupElementTest.java

.../java/test/junit/net/i2p/crypto/eddsa/math/MathUtils.java

.../net/i2p/crypto/eddsa/math/PrecomputationTestVectors.java

.../crypto/eddsa/math/bigint/BigIntegerFieldElementTest.java

...i2p/crypto/eddsa/math/bigint/BigIntegerScalarOpsTest.java

...2p/crypto/eddsa/math/ed25519/Ed25519FieldElementTest.java

...it/net/i2p/crypto/eddsa/spec/EdDSAPrivateKeySpecTest.java