msoleps is not goroutine safe

[persol-makise]

Hi,

I'm using this library to convert doc files into text using multiple goroutines, but I encountered the error below,

fatal error: concurrent map writes
goroutine 22096 [running]:
github.com/richardlehane/msoleps.addDefaults(...)
        /go/pkg/mod/github.com/richardlehane/msoleps@v1.0.3/sets.go:20
github.com/richardlehane/msoleps.(*Reader).start(0xc003e0ef78, {0x142a840?, 0xc0028fc000?})
        /go/pkg/mod/github.com/richardlehane/msoleps@v1.0.3/msoleps.go:125 +0x2de
github.com/richardlehane/msoleps.(*Reader).Reset(...)
        /go/pkg/mod/github.com/richardlehane/msoleps@v1.0.3/msoleps.go:76
code.sajari.com/docconv/v2.ConvertDoc.func1()
        /go/pkg/mod/code.sajari.com/docconv/v2@v2.0.0-pre.3/doc.go:44 +0x147
created by code.sajari.com/docconv/v2.ConvertDoc in goroutine 21884
        /go/pkg/mod/code.sajari.com/docconv/v2@v2.0.0-pre.3/doc.go:25 +0x178

I'm using v2.0.0-pre.3