This closes qax-os#1874, reduces memory usage for the GetRows function (

qax-os#1875)

- Avoid allocate memory for reading continuously empty rows on the tail of the worksheet

rows.go

@@ -70,8 +70,11 @@ func (f *File) GetRows(sheet string, opts ...Options) ([][]string, error) {
 		if err != nil {
 			break
 		}
-		results = append(results, row)
 		if len(row) > 0 {
+			if emptyRows := cur - maxVal - 1; emptyRows > 0 {
+				results = append(results, make([][]string, emptyRows)...)
+			}
+			results = append(results, row)
 			maxVal = cur
 		}
 	}