descriptor: add unit test demonstrating sanity-checking behavior in <= 12.x

See rust-bitcoin#734 for
discussion of this. Meanwhile, add a unit test so we can determine when
the behavior changes.

Author: apoelstra

src/descriptor/mod.rs

@@ -2011,6 +2011,22 @@ pk(03f28773c2d975288bc7d1d205c3748651b075fbc6610e58cddeeddf8f19405aa8))";
         Descriptor::<DescriptorPublicKey>::from_str("wsh(andor(pk(tpubDEN9WSToTyy9ZQfaYqSKfmVqmq1VVLNtYfj3Vkqh67et57eJ5sTKZQBkHqSwPUsoSskJeaYnPttHe2VrkCsKA27kUaN9SDc5zhqeLzKa1rr/0'/<0;1;2;3>/*),older(10000),pk(tpubD8LYfn6njiA2inCoxwM7EuN3cuLVcaHAwLYeups13dpevd3nHLRdK9NdQksWXrhLQVxcUZRpnp5CkJ1FhE61WRAsHxDNAkvGkoQkAeWDYjV/8/<0;1;2>/*)))").unwrap_err();
     }
 
+    #[test]
+    fn regression_734() {
+        Descriptor::<DescriptorPublicKey>::from_str(
+            "wsh(or_i(pk(0202baaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa0a66a),1))",
+        )
+        .unwrap();
+        Descriptor::<DescriptorPublicKey>::from_str(
+            "sh(or_i(pk(0202baaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa0a66a),1))",
+        )
+        .unwrap();
+        Descriptor::<DescriptorPublicKey>::from_str(
+            "tr(02baaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa0a66a,1)",
+        )
+        .unwrap_err();
+    }
+
     #[test]
     fn test_context_pks() {
         let comp_key = bitcoin::PublicKey::from_str(