RPC validateaddress: test pwalletMain for NULL (no-wallet mode)

Conflicts:
	src/rpcwallet.cpp

Rebased-from: b878f6a92436e3facd700e2e10c04f541cd6421b

src/rpcwallet.cpp

@@ -1524,13 +1524,13 @@ Value validateaddress(const Array& params, bool fHelp)
         CTxDestination dest = address.Get();
         string currentAddress = address.ToString();
         ret.push_back(Pair("address", currentAddress));
-        bool fMine = IsMine(*pwalletMain, dest);
+        bool fMine = pwalletMain ? IsMine(*pwalletMain, dest) : false;
         ret.push_back(Pair("ismine", fMine));
         if (fMine) {
             Object detail = boost::apply_visitor(DescribeAddressVisitor(), dest);
             ret.insert(ret.end(), detail.begin(), detail.end());
         }
-        if (pwalletMain->mapAddressBook.count(dest))
+        if (pwalletMain && pwalletMain->mapAddressBook.count(dest))
             ret.push_back(Pair("account", pwalletMain->mapAddressBook[dest]));
     }
     return ret;