blame: prevent a segv when -L given start > EOF

blame would segv if given -L <lineno> with <lineno> past the end of the file.
While we're fixing the bug, add test cases for an invalid <start> when called
as -L <start>,<end> or -L<start>.

Signed-off-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-blame.c

@@ -2432,7 +2432,7 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
 	if (top < 1)
 		top = lno;
 	bottom--;
-	if (lno < top)
+	if (lno < top || lno < bottom)
 		die("file %s has only %lu lines", path, lno);
 
 	ent = xcalloc(1, sizeof(*ent));

t/t8003-blame.sh

@@ -157,4 +157,12 @@ EOF
   git --no-pager blame $COMMIT -- uno >/dev/null
 '
 
+test_expect_success 'blame -L with invalid start' '
+	test_must_fail git blame -L5 tres 2>&1 | grep "has only 2 lines"
+'
+
+test_expect_success 'blame -L with invalid end' '
+	git blame -L1,5 tres 2>&1 | grep "has only 2 lines"
+'
+
 test_done