fix: fix CancelRow() causing data corruption if called after send exception

src/net-questdb-client-tests/HttpTests.cs

@@ -993,6 +993,33 @@ public async Task CancelLine()
         Assert.That(srv.PrintBuffer(), Is.EqualTo(expected));
     }
 
+
+    [Test]
+    public async Task CancelLineAfterClear()
+    {
+        using var srv = new DummyHttpServer();
+        await srv.StartAsync(HttpPort);
+        using var sender = Sender.New($"http::addr={Host}:{HttpPort};auto_flush=off;");
+
+        sender.Table("good");
+        sender.Symbol("asdf", "sdfad");
+        sender.Column("ddd", 123);
+        sender.At(new DateTime(1970, 1, 2));
+
+        sender.Table("bad");
+        sender.Symbol("asdf", "sdfad");
+        sender.Column("asdf", 123);
+        sender.Clear();
+        sender.CancelRow();
+
+        sender.Table("good");
+        await sender.AtAsync(new DateTime(1970, 1, 2));
+        await sender.SendAsync();
+
+        var expected = "good 86400000000000\n";
+        Assert.That(srv.PrintBuffer(), Is.EqualTo(expected));
+    }
+
     [Test]
     public async Task CannotConnect()
     {

src/net-questdb-client/Buffers/BufferV1.cs

@@ -135,11 +135,13 @@ public void Clear()
             _buffers[i] = (_buffers[i].Buffer, 0);
         }
 
-        Position          = 0;
-        RowCount          = 0;
-        Length            = 0;
-        WithinTransaction = false;
-        _currentTableName = "";
+        Position              = 0;
+        RowCount              = 0;
+        Length                = 0;
+        WithinTransaction     = false;
+        _currentTableName     = "";
+        _lineStartBufferIndex = 0;
+        _lineStartBufferPosition = 0;
     }
 
     /// <inheritdoc />