Fix access violation when using Express user instances (#2101)

Author: emidah

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlConnectionString.cs

@@ -703,6 +703,7 @@ internal SqlConnectionString(SqlConnectionString connectionOptions, string dataS
             _attestationProtocol = connectionOptions._attestationProtocol;
             _serverSPN = connectionOptions._serverSPN;
             _failoverPartnerSPN = connectionOptions._failoverPartnerSPN;
+            _hostNameInCertificate = connectionOptions._hostNameInCertificate;
 #if NETFRAMEWORK
             _connectionReset = connectionOptions._connectionReset;
             _contextConnection = connectionOptions._contextConnection;

src/Microsoft.Data.SqlClient/tests/FunctionalTests/SqlConnectionTest.cs

@@ -945,6 +945,15 @@ public void Open_ConnectionString_Whitespace()
             Assert.NotNull(ex.Message);
         }
 
+        [Fact]
+        public void Open_ConnectionString_UserInstance()
+        {
+            SqlConnection cn = new SqlConnection("User Instance=true;");
+            SqlException ex = Assert.Throws<SqlException>(() => cn.Open());
+            // Throws without access violation
+            Assert.NotNull(ex.Message);
+        }
+
         [Fact]
         public void ServerVersion_Connection_Closed()
         {