Fix loop flag setting for mods with very small loops

Reported by Misty De Meo:

"I noticed incorrect audio playback when playing back a ProTracker
module called r@4321.mod. The song opens with one channel playing back
a beeping noise when rendered with players like UADE; in XMP, this
channel is rendered as just a soft clicking noise.

The song can be found on Modland:
http://files.exotica.org.uk/modland/?file=pub/modules/Protracker/Muffler/r%404321.mod"

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Update Changelog

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>