ReadStream: incorrect validation of range.endPos when endPos is 0

[lkho]

when specifying { endPos: 0 }, it is converted to position - 1. However, it is indeed valid since startPos/endPos is inclusive.

gridfs-stream/lib/readstream.js

Lines 117 to 123 in c394e05

	if (err) return self._error(err);
	// Calculate the correct end position either from EOF or end of range. Also handle incorrect range request.
	if (!self.range.endPos || self.range.endPos > position-1) {self.range.endPos = position - 1};
	// Set the read head to the beginning of the file or start position if specified
	self._store.seek(self.range.startPos, self._grid.mongo.GridStore.IO_SEEK_SET, function(err) {