blame: reject empty ranges -LX,+0 and -LX,-0

Empty ranges -LX,+0 and -LX,-0 are nonsensical in the context of blame
yet they are accepted (in fact, both are interpreted as -LX,+2).  Report
them as invalid.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

line-range.c

@@ -26,6 +26,8 @@ static const char *parse_loc(const char *spec, nth_line_fn_t nth_line,
 		if (term != spec + 1) {
 			if (!ret)
 				return term;
+			if (num == 0)
+				die("-L invalid empty range");
 			if (spec[0] == '-')
 				num = 0 - num;
 			if (0 < num)

t/annotate-tests.sh

@@ -185,7 +185,7 @@ test_expect_success 'blame -L Y,X (undocumented)' '
 	check_count -L6,3 B 1 B1 1 B2 1 D 1
 '
 
-test_expect_failure 'blame -L X,+0' '
+test_expect_success 'blame -L X,+0' '
 	test_must_fail $PROG -L1,+0 file
 '
 
@@ -197,7 +197,7 @@ test_expect_success 'blame -L X,+N' '
 	check_count -L3,+4 B 1 B1 1 B2 1 D 1
 '
 
-test_expect_failure 'blame -L X,-0' '
+test_expect_success 'blame -L X,-0' '
 	test_must_fail $PROG -L1,-0 file
 '