line-log: fix "log -LN" crash when N is last line of file

range-set invariants are: ranges must be (1) non-empty, (2) disjoint,
(3) sorted in ascending order.

line_log_data_insert() breaks the non-empty invariant under the
following conditions: the incoming range is empty and the pathname
attached to the range has not yet been encountered. In this case,
line_log_data_insert() assigns the empty range to a new line_log_data
record without taking any action to ensure that the empty range is
eventually folded out.  Subsequent range-set functions crash or throw an
assertion failure upon encountering such an anomaly.  Fix this bug.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Acked-by: Thomas Rast <trast@inf.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: sunshineco

line-log.c

@@ -299,6 +299,7 @@ static void line_log_data_insert(struct line_log_data **list,
 	p = xcalloc(1, sizeof(struct line_log_data));
 	p->path = path;
 	range_set_append(&p->ranges, begin, end);
+	sort_and_merge_range_set(&p->ranges);
 	if (ip) {
 		p->next = ip->next;
 		ip->next = p;

t/t4211-line-log.sh

@@ -73,7 +73,7 @@ test_expect_success '-L {empty-range} (any -L)' '
 	git log -L1,1:b.c -L$n:b.c
 '
 
-test_expect_failure '-L {empty-range} (first -L)' '
+test_expect_success '-L {empty-range} (first -L)' '
 	n=$(expr $(wc -l <b.c) + 1) &&
 	git log -L$n:b.c
 '