[PATCH v2] line-range: Fix infinite loop bug with degenerate regex

[Lars Kellogg-Stedman <lars@oddbit.com>]

When the -L argument to "git log" is passed the degenerate regular
expression "$" (as in "-L :$:line-range.c"), this results in an
infinite loop in find_funcname_matching_regexp() (the function
iterates through the file correctly, but when it reaches the end of
the file it matches $ against the empty string, "", and at that points
loops forever).

Modify the loop condition from while (1) to while (*start) so that the
loop exits when start is the empty string. In this case, "git log" exits
with the error:

    fatal: -L parameter '$' starting at line 1: no match

Originally reported in <https://stackoverflow.com/q/74690545/147356>.

Signed-off-by: Lars Kellogg-Stedman <lars@oddbit.com>
---
 line-range.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/line-range.c b/line-range.c
index 955a8a9535..bdcb810485 100644
--- a/line-range.c
+++ b/line-range.c
@@ -135,7 +135,7 @@ static const char *find_funcname_matching_regexp(xdemitconf_t *xecfg, const char
 {
 	int reg_error;
 	regmatch_t match[1];
-	while (1) {
+	while (*start) {
 		const char *bol, *eol;
 		reg_error = regexec(regexp, start, 1, match, 0);
 		if (reg_error == REG_NOMATCH)
@@ -161,6 +161,8 @@ static const char *find_funcname_matching_regexp(xdemitconf_t *xecfg, const char
 			return bol;
 		start = eol;
 	}
+
+    return NULL;
 }
 
 static const char *parse_range_funcname(
-- 
2.38.1