compareTo(): Return 0 if other is the same

Author: vanitasvitae

pg/src/main/java/org/bouncycastle/openpgp/api/OpenPGPCertificate.java

@@ -3010,6 +3010,11 @@ public String toString()
         @Override
         public int compareTo(OpenPGPSignatureChain other)
         {
+            if (this == other)
+            {
+                return 0;
+            }
+
             if (isHardRevocation())
             {
                 return -1;