Preserve mac after doFinal

Author: peterdettman

core/src/main/java/org/bouncycastle/crypto/engines/Grain128AEADEngine.java

@@ -322,9 +322,17 @@ public int processBytes(byte[] input, int inOff, int len, byte[] output,
     }
 
     public void reset()
+    {
+        reset(true);
+    }
+
+    private void reset(boolean clearMac)
     {
         this.isEven = true;
-        this.mac = null;
+        if (clearMac)
+        {
+            this.mac = null;
+        }
         this.aadData.reset();
         this.aadFinished = false;
         setKey(workingKey, workingIV);
@@ -487,14 +495,9 @@ public int doFinal(byte[] out, int outOff)
 
         System.arraycopy(mac, 0, out, outOff, mac.length);
 
-        try
-        {
-            return mac.length;
-        }
-        finally
-        {
-            reset();
-        }
+        reset(false);
+
+        return mac.length;
     }
 
     public byte[] getMac()