Some DLINK camera fail the content type check

[kand617]

I came across a dlink camera who's content type is multipart/x-mixed-replace;boundary=video boundary--

This fails to parse as the -- is not valid unless its in quotes. Thus we need a way to sanitize the header to get `multipart/x-mixed-replace;boundary="video boundary--" (quotes added)

The following might be sufficient

func SanitizeContentType(s string) string {
    if strings.HasSuffix(s, "-") {
        // Boundary is not escaped
        segments:= strings.Split(s, "boundary=")
        formatted := segments[0] + "boundary=\"" + segments[1] + "\""
        return formatted
    }
    return s
}