PGPSignature: Use proper method to update signature with salt

CANONICAL_TEXT signatures update() would handle 'd0' specially,
resulting in broken signature verification if salt contained 'd0'.
With this patch, we push salt to sigOut directly.

pg/src/main/java/org/bouncycastle/openpgp/PGPSignature.java

@@ -191,10 +191,18 @@ private void checkSaltSize()
     }
 
     private void updateWithSalt()
+            throws PGPException
     {
         if (getVersion() == SignaturePacket.VERSION_6)
         {
-            update(sigPck.getSalt());
+            try
+            {
+                sigOut.write(sigPck.getSalt());
+            }
+            catch (IOException e)
+            {
+                throw new PGPException("Cannot update signature with salt.", e);
+            }
         }
     }