ensuring the original invariant array is copied and can not be modified

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>

src/main/org/openscience/cdk/hash/PerturbedAtomHashGenerator.java

@@ -166,7 +166,7 @@ private long[] generate(IAtomContainer container, long[] seeds,
             encoder.reset();
 
             // compute new hash codes and copy the values a column in the matrix
-            long[] tmp = basic.generate(original, encoder, graph);
+            long[] tmp = basic.generate(copy(original), encoder, graph);
             for (int j = 0; j < n; j++) {
                 perturbed[j][i + 1] = tmp[j];
             }