refactor: simplify exception handling and streamline header assignment in response

Author: codelove1314

src/Magicodes.ExporterAndImporter.AspNetCore/Extensions/MagicodesBase.cs

@@ -62,7 +62,7 @@ public async Task<bool> HandleSuccessfulReqeustAsync(HttpContext context, object
             }
             if (contentType != "")
             {
-                context.Response.Headers.Add("Content-Disposition", $"attachment;filename={filename}");
+                context.Response.Headers["Content-Disposition"] = $"attachment;filename={filename}";
                 context.Response.ContentType = contentType;
                 if (result != null)
                 {

src/Magicodes.ExporterAndImporter.Excel.AspNetCore/XlsxFileResultBase.cs

@@ -35,9 +35,8 @@ protected virtual async Task DownloadExcelFileAsync(ActionContext context,
                 downloadFileName += ".xlsx";
             }
 
-            context.HttpContext.Response.Headers.Add("Content-Disposition", new[] {
-                "attachment; filename=" +HttpUtility.UrlEncode(downloadFileName)
-            });
+            context.HttpContext.Response.Headers["Content-Disposition"] = 
+                "attachment; filename=" + HttpUtility.UrlEncode(downloadFileName);
             await stream.CopyToAsync(context.HttpContext.Response.Body);
         }
     }

src/Magicodes.ExporterAndImporter.Excel/Utility/TemplateExport/TemplateExportHelper.cs

@@ -740,7 +740,7 @@ private bool RenderCellPipeline(Interpreter target, ExcelWorksheet sheet, ref st
                                         excelImage.SetSize(width, height);
                                     }
                                 }
-                                catch (Exception ex)
+                                catch
                                 {
                                     cell.Value = alt;
                                 }