Fix file corrupted in some cases, check file extension and format code

Fix file corrupted when save as in XLAM / XLSM / XLTM / XLTX extension in some case
New exported error ErrWorkbookExt has been added, and check file extension on save the workbook
Format source code with `gofumpt`

1 files changed, 1 insertions, 1 deletions

diff --git a/sheet_test.go b/sheet_test.go
index a5c99a6..7df9018 100644
--- a/sheet_test.go
+++ b/sheet_test.go
@@ -123,7 +123,6 @@ func TestPageLayoutOption(t *testing.T) {
 
 	for i, test := range testData {
 		t.Run(fmt.Sprintf("TestData%d", i), func(t *testing.T) {
-
 			opt := test.nonDefault
 			t.Logf("option %T", opt)
 
@@ -452,6 +451,7 @@ func BenchmarkNewSheet(b *testing.B) {
 		}
 	})
 }
+
 func newSheetWithSet() {
 	file := NewFile()
 	file.NewSheet("sheet1")