Description

Steps to reproduce the issue:

1. xlsx, err = excelize.OpenReader(resp.Body)
2. sheetName := xlsx.GetSheetName(xlsx.GetActiveSheetIndex())
3. rows, err = xlsx.GetRows(sheetName)

Describe the results you received:
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xb2c055]
goroutine 82
[running]:
github.com/360EntSecGroup-Skylar/excelize/v2.(*xlsxC).getValueFrom(0xc0103d1348, 0xc0000ffb00, 0xc0002b80a0, 0x1, 0x0, 0x0, 0xc0103d1310)
/data/wubin/gopath/pkg/mod/github.com/360!ent!sec!group-!skylar/excelize/v2@v2.0.2/rows.go:214 +0xe5
github.com/360EntSecGroup-Skylar/excelize/v2.(*Rows).Columns(0xc03612e000, 0x0, 0x40, 0xc00013c000, 0x0, 0x0)
/data/wubin/gopath/pkg/mod/github.com/360!ent!sec!group-!skylar/excelize/v2@v2.0.2/rows.go:80 +0x1c9
github.com/360EntSecGroup-Skylar/excelize/v2.(*File).GetRows(0xc0000ffb00, 0xc000392360, 0x6, 0x1, 0x1, 0x14, 0x0, 0x0)
/data/wubin/gopath/pkg/mod/github.com/360!ent!sec!group-!skylar/excelize/v2@v2.0.2/rows.go:41 +0xe4
Describe the results you expected:
no panic and get rows
Output of go version:

go version go1.12.6 linux/amd64

Excelize version or commit ID:

v2.0.2

Environment details (OS, Microsoft Excel™ version, physical, etc.):