Fix #539 Fixed error opening excel file created in encoding d… (#540)

* Fixed issue #539 Fixed error opening excel file created in encoding different from UTF-8, added logging of possible errors when decoding XML if the function does not provide exit with an error

* Added test for CharsetReader

* Fixed #discussion_r359397878

Discussion: https://github.com/360EntSecGroup-Skylar/excelize/pull/540#discussion_r359397878

* Fixed go fmt

* go mod tidy and removed unused imports

* The code has been refactored

1 files changed, 17 insertions, 6 deletions

diff --git a/comment.go b/comment.go
index 7f3b10d..99630c9 100644
--- a/comment.go
+++ b/comment.go
@@ -10,9 +10,12 @@
 package excelize
 
 import (
+	"bytes"
 	"encoding/json"
 	"encoding/xml"
 	"fmt"
+	"io"
+	"log"
 	"strconv"
 	"strings"
 )
@@ -303,12 +306,16 @@ func (f *File) countComments() int {
 // decodeVMLDrawingReader provides a function to get the pointer to the
 // structure after deserialization of xl/drawings/vmlDrawing%d.xml.
 func (f *File) decodeVMLDrawingReader(path string) *decodeVmlDrawing {
+	var err error
+
 	if f.DecodeVMLDrawing[path] == nil {
 		c, ok := f.XLSX[path]
 		if ok {
-			d := decodeVmlDrawing{}
-			_ = xml.Unmarshal(namespaceStrictToTransitional(c), &d)
-			f.DecodeVMLDrawing[path] = &d
+			f.DecodeVMLDrawing[path] = new(decodeVmlDrawing)
+			if err = f.xmlNewDecoder(bytes.NewReader(namespaceStrictToTransitional(c))).
+				Decode(f.DecodeVMLDrawing[path]); err != nil && err != io.EOF {
+				log.Printf("xml decode error: %s", err)
+			}
 		}
 	}
 	return f.DecodeVMLDrawing[path]
@@ -328,12 +335,16 @@ func (f *File) vmlDrawingWriter() {
 // commentsReader provides a function to get the pointer to the structure
 // after deserialization of xl/comments%d.xml.
 func (f *File) commentsReader(path string) *xlsxComments {
+	var err error
+
 	if f.Comments[path] == nil {
 		content, ok := f.XLSX[path]
 		if ok {
-			c := xlsxComments{}
-			_ = xml.Unmarshal(namespaceStrictToTransitional(content), &c)
-			f.Comments[path] = &c
+			f.Comments[path] = new(xlsxComments)
+			if err = f.xmlNewDecoder(bytes.NewReader(namespaceStrictToTransitional(content))).
+				Decode(f.Comments[path]); err != nil && err != io.EOF {
+				log.Printf("xml decode error: %s", err)
+			}
 		}
 	}
 	return f.Comments[path]