tests: Fix dangling pwalletMain pointer in wallet tests

src/wallet/test/wallet_tests.cpp

@@ -397,6 +397,7 @@ BOOST_FIXTURE_TEST_CASE(rescan, TestChain100Setup)
 
     {
         CWallet wallet;
+        CWallet *backup = ::pwalletMain;
         ::pwalletMain = &wallet;
         UniValue key;
         key.setObject();
@@ -412,6 +413,7 @@ BOOST_FIXTURE_TEST_CASE(rescan, TestChain100Setup)
 
         UniValue response = importmulti(request);
         BOOST_CHECK_EQUAL(response.write(), strprintf("[{\"success\":false,\"error\":{\"code\":-1,\"message\":\"Failed to rescan before time %d, transactions may be missing.\"}}]", newTip->GetBlockTimeMax()));
+        ::pwalletMain = backup;
     }
 }