TTL / PTTL commands: two bugs fixed.

This commit fixes two corner cases for the TTL command.

1) When the key was already logically expired (expire time older
than current time) the command returned -1 instead of -2.

2) When the key was existing and the expire was found to be exactly 0
(the key was just about to expire), the command reported -1 (that is, no
expire) instead of a TTL of zero (that is, about to expire).

src/db.c

@@ -612,17 +612,17 @@ void pexpireatCommand(redisClient *c) {
 void ttlGenericCommand(redisClient *c, int output_ms) {
     long long expire, ttl = -1;
 
-    expire = getExpire(c->db,c->argv[1]);
     /* If the key does not exist at all, return -2 */
-    if (expire == -1 && lookupKeyRead(c->db,c->argv[1]) == NULL) {
+    if (lookupKeyRead(c->db,c->argv[1]) == NULL) {
         addReplyLongLong(c,-2);
         return;
     }
     /* The key exists. Return -1 if it has no expire, or the actual
      * TTL value otherwise. */
+    expire = getExpire(c->db,c->argv[1]);
     if (expire != -1) {
         ttl = expire-mstime();
-        if (ttl < 0) ttl = -1;
+        if (ttl < 0) ttl = 0;
     }
     if (ttl == -1) {
         addReplyLongLong(c,-1);