Oops. You're right for little-endian encoders. (See another comment on this thread for a simple bijective big-endian encoder I whipped up just now.) I've always written big-endian encoders or bijective big-endian encoders, so that byte strings sort the same lexographically and numerically.

Though, a simple loop encoder and decoder are still easily doable if the unary length encoding is in the most significant bits. You're right, though, for a little-endian encoder, it's a slightly more simple to put the unary length encoding in the least significant bits.