AddPicture (autofit) has a size problem when there are multiple merged cells.

[yuki2006]

Thank you for the very useful library.

Description

Depending on the order of the merged cells,
The size of the image changes because the cell merge detection cannot be performed.

Probably the line is wrong and the inMergeCell is overwritten and it is not judged correctly.

https://github.com/360EntSecGroup-Skylar/excelize/blob/master/picture.go#L608

Steps to reproduce the issue:
1.

		f := excelize.NewFile()
		sheet1 := f.GetSheetName(0)

		f.MergeCell(sheet1, "A2", "C3")
		f.MergeCell(sheet1, "A100", "C101")

		err := f.AddPicture(sheet1, "A2", "../../.ignore/Pic.jpg", `{"lock_aspect_ratio":true,"autofit":true}`)
		if err != nil {
			t.Error(err)
			return
		}

		f.SaveAs("/tmp/A.xlsx")

		f := excelize.NewFile()
		sheet1 := f.GetSheetName(0)

		f.MergeCell(sheet1, "A100", "C101")
		f.MergeCell(sheet1, "A2", "C3")

		err := f.AddPicture(sheet1, "A2", "../../.ignore/Pic.jpg", `{"lock_aspect_ratio":true,"autofit":true}`)
		if err != nil {
			t.Error(err)
			return
		}

		f.SaveAs("/tmp/B.xlsx")

Describe the results you expected:

Display pattern 2 regardless of the order of merged cells.

Output of go version:

go1.15

Excelize version or commit ID:

v2.3.1

[xuri]

Hi, @yuki2006. Thanks for your issue. I have fixed it, please try to use the master branch code, and this patch will be released in the next version.