Correct handling of "Range:" request header. Replaces buggy implementation (480b1e8, 44ab090) that was recently backed out.
NOTE: Does not yet support multiple ranges (e.g. "bytes=1-10,20-30") because that requires sending a multipart response, which is more complex than I want to get into now.
Signed-off-by: Konstantin Haase <email@example.com>