zenlei

### Describe the bug panic: runtime error: invalid memory address or nil pointer dereference [signal SIGSEGV: segmentation violation code=0x1 addr=0x28 pc=0x118612e] goroutine 15 [running]: github.com/gabriel-vasile/mimetype.(*MIME).Extension(...) github.com/gabriel-vasile/[email protected]/mime.go:32 github.com/iyear/tdl/core/tmedia.GetDocumentName(0xc000349cc0) github.com/iyear/tdl/[email protected]/tmedia/document.go:37 +0x6e github.com/iyear/tdl/core/tmedia.GetDocumentInfo(0x64?)...