This closes #1628, fix the GetPictures function returns pictures doesn't correct in some cases

Author: xuri

picture.go

@@ -649,9 +649,7 @@ func (f *File) getPicture(row, col int, drawingXML, drawingRelationships string)
 	if wsDr, _, err = f.drawingParser(drawingXML); err != nil {
 		return
 	}
-	if pics = f.getPicturesFromWsDr(row, col, drawingRelationships, wsDr); len(pics) > 0 {
-		return
-	}
+	pics = f.getPicturesFromWsDr(row, col, drawingRelationships, wsDr)
 	deWsDr = new(decodeWsDr)
 	if err = f.xmlNewDecoder(bytes.NewReader(namespaceStrictToTransitional(f.readXML(drawingXML)))).
 		Decode(deWsDr); err != nil && err != io.EOF {

picture_test.go

@@ -70,6 +70,15 @@ func TestAddPicture(t *testing.T) {
 	assert.NoError(t, f.SaveAs(filepath.Join("test", "TestAddPicture1.xlsx")))
 	assert.NoError(t, f.Close())
 
+	// Test get pictures after inserting a new picture from a workbook which contains existing pictures
+	f, err = OpenFile(filepath.Join("test", "TestAddPicture1.xlsx"))
+	assert.NoError(t, err)
+	assert.NoError(t, f.AddPicture("Sheet1", "A30", filepath.Join("test", "images", "excel.jpg"), nil))
+	pics, err := f.GetPictures("Sheet1", "A30")
+	assert.NoError(t, err)
+	assert.Len(t, pics, 2)
+	assert.NoError(t, f.Close())
+
 	// Test add picture with unsupported charset content types
 	f = NewFile()
 	f.ContentTypes = nil