libarchive-3.3.2: Fix CVE-2017-14166

[No upstream tracking] -- https://github.com/libarchive/libarchive/pull/935

archive_read_support_format_xar: heap-based buffer overflow in xml_data

Upstream-Status: Backport [https://github.com/libarchive/libarchive/commit/fa7438a0ff4033e4741c807394a9af6207940d71]
CVE: CVE-2017-14166
Bug: 935
Signed-off-by: Andrej Valek <andrej.valek@siemens.com>

diff --git a/libarchive/archive_read_support_format_xar.c b/libarchive/archive_read_support_format_xar.c
index 7a22beb..93eeacc 100644
--- a/libarchive/archive_read_support_format_xar.c
+++ b/libarchive/archive_read_support_format_xar.c
@@ -1040,6 +1040,9 @@ atol10(const char *p, size_t char_cnt)
 	uint64_t l;
 	int digit;
 
+	if (char_cnt == 0)
+		return (0);
+
 	l = 0;
 	digit = *p - '0';
 	while (digit >= 0 && digit < 10  && char_cnt-- > 0) {
@@ -1054,7 +1057,10 @@ atol8(const char *p, size_t char_cnt)
 {
 	int64_t l;
 	int digit;
-        
+
+	if (char_cnt == 0)
+		return (0);
+
 	l = 0;
 	while (char_cnt-- > 0) {
 		if (*p >= '0' && *p <= '7')