changed ML-DSA/SLH-DSA Jca signatures to return null if default 0 length context is used, relates to github #1946.

Author: dghgit

prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/util/BaseDeterministicOrRandomSignature.java

@@ -162,7 +162,7 @@ protected final AlgorithmParameters engineGetParameters()
     {
         if (engineParams == null)
         {
-            if (paramSpec != null)
+            if (paramSpec != null && paramSpec != ContextParameterSpec.EMPTY_CONTEXT_SPEC)
             {
                 try
                 {

prov/src/test/java/org/bouncycastle/pqc/jcajce/provider/test/MLDSATest.java

@@ -531,10 +531,8 @@ public void testHashMLDSAKATSig()
         assertTrue(sig.verify(genS));
 
         AlgorithmParameters algP = sig.getParameters();
-
-        ContextParameterSpec cSpec = algP.getParameterSpec(ContextParameterSpec.class);
-
-        assertTrue(Arrays.areEqual(new byte[0], cSpec.getContext()));
+        
+        assertTrue(null == algP);
 
         // test using ml-dsa-44 for the key, should be the same.