descriptor: never ignore the return value when deriving an extended key

In some cases we asserted it succeeded, in others we were just ignoring it

src/script/descriptor.cpp

@@ -328,7 +328,7 @@ class BIP32PubkeyProvider final : public PubkeyProvider
     {
         if (!GetExtKey(arg, xprv)) return false;
         for (auto entry : m_path) {
-            xprv.Derive(xprv, entry);
+            if (!xprv.Derive(xprv, entry)) return false;
             if (entry >> 31) {
                 last_hardened = xprv;
             }
@@ -498,8 +498,8 @@ public:
         CExtKey extkey;
         CExtKey dummy;
         if (!GetDerivedExtKey(arg, extkey, dummy)) return false;
-        if (m_derive == DeriveType::UNHARDENED) extkey.Derive(extkey, pos);
-        if (m_derive == DeriveType::HARDENED) extkey.Derive(extkey, pos | 0x80000000UL);
+        if (m_derive == DeriveType::UNHARDENED && !extkey.Derive(extkey, pos)) return false;
+        if (m_derive == DeriveType::HARDENED && !extkey.Derive(extkey, pos | 0x80000000UL)) return false;
         key = extkey.key;
         return true;
     }

src/test/descriptor_tests.cpp

@@ -233,7 +233,7 @@ void DoCheck(const std::string& prv, const std::string& pub, const std::string&
                 for (const auto& xpub_pair : parent_xpub_cache) {
                     const CExtPubKey& xpub = xpub_pair.second;
                     CExtPubKey der;
-                    xpub.Derive(der, i);
+                    BOOST_CHECK(xpub.Derive(der, i));
                     pubkeys.insert(der.pubkey);
                 }
                 int count_pks = 0;
@@ -265,7 +265,7 @@ void DoCheck(const std::string& prv, const std::string& pub, const std::string&
                     const CExtPubKey& xpub = xpub_pair.second;
                     pubkeys.insert(xpub.pubkey);
                     CExtPubKey der;
-                    xpub.Derive(der, i);
+                    BOOST_CHECK(xpub.Derive(der, i));
                     pubkeys.insert(der.pubkey);
                 }
                 int count_pks = 0;