Merge 07ec589dd3 into 1cc1536e6a

When detecting that zero is single, code reads the next group even if it is last group.

If next bytes are not-null, last zero is not omitted.

If next bytes are null, last zero is omitted, but since there are no groups left,
finishing ':' will not be written, resulting in invalid address.

This commit turns off non-single zero check for the last group.

test/unit/ip6/test_ip6.c

@@ -279,7 +279,7 @@ START_TEST(test_ip6_ntoa)
     {IPADDR6_INIT_HOST(0xfe800000, 0xff000000, 0xb2a1a2ff, 0xfea3a4a5), 0, "FE80:0:FF00:0:B2A1:A2FF:FEA3:A4A5"}, /* don't omit single zero blocks */
     {IPADDR6_INIT_HOST(0xfe800000, 0xff000000, 0xb2000000, 0x0000a4a5), 0, "FE80:0:FF00:0:B200::A4A5"}, /* omit longest zero block */
     {IPADDR6_INIT_HOST(0x20010db8, 0x00010002, 0x00030004, 0x00050000), 0, "2001:DB8:1:2:3:4:5:0"}, /* do not omit last zero due to out-of-bounds bug */
-    {IPADDR6_INIT_HOST(0x20010db8, 0x00010002, 0x00030004, 0x00050000), ~0, "2001:DB8:1:2:3:4:5:0"}, /* do not omit last zero due to out-of-bounds bug */
+    {IPADDR6_INIT_HOST(0x20010db8, 0x00010002, 0x00030004, 0x00050000), 1, "2001:DB8:1:2:3:4:5:0"}, /* do not omit last zero due to out-of-bounds bug */
   };
   char buf[128];
   char *str;