Handling DataTable Error: There is no row at position 0 in C# and VB.Net

Hi i have a dropdown select that selects and updates label, my challenge is that if there is no roll when the dropdown is selected it will show this error 

Server Error in '/' Application.
There is no row at position 0.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.IndexOutOfRangeException: There is no row at position 0.

Source Error:


Line 70:         Panel pn = (Panel)ddlCategory.FindControl("Panel2");
Line 71:         pn.Visible = true;
Line 72:         lblMessage2.Text = dt.Rows[0]["Quantity_Remaining"].ToString();
Line 73:         //Label lblMessage2 = (Label)ddlitem.FindControl("ltText");
Line 74: 

code

so my question is how do i display a nice message to the user that there is no item row to display instead of showing this error

code 

    protected void ddlCategory_SelectedIndexChanged(object sender, EventArgs e)
    {
        DataTable dt = GetDataTable("SELECT Quantity_Remaining FROM MainWareHouse WHERE Category = '" + ddlCategory.SelectedItem.Text.Trim() + "'");
        // DataTable dt2 = GetDataTable("SELECT Debt FROM CustomerDetail WHERE CustomerPhone = '" + ddlcustomerphone.SelectedItem.Text.Trim() + "'");
        // lblOlDebt.Text = dt.Rows[0]["Debt"].ToString();

        //lblQuantityAvailable.Text = dt.Rows[0]["Rows_In_Carton"].ToString();
        Panel pn = (Panel)ddlCategory.FindControl("Panel2");
        pn.Visible = true;
        lblMessage2.Text = dt.Rows[0]["Quantity_Remaining"].ToString();
        //Label lblMessage2 = (Label)ddlitem.FindControl("ltText");