parse_npt_range: fix parsing of stop values

parse_range_part() isn't supposed to read any extra char after the range to
parse.

Fix regression in unit test introduced by
edd212d62d6135fe80e4be033a577ba13b13553e.
parse_npt_range: init output variable

Fix regression in unit test introduced by
edd212d62d6135fe80e4be033a577ba13b13553e
Merge pull request #139 from gdesmott/fix-test

Fix test