Fix incorrect comments

error != success; and 0 != number of bytes written

Closes #1806

src/aof.c

@@ -549,7 +549,7 @@ void freeFakeClient(struct redisClient *c) {
     zfree(c);
 }
 
-/* Replay the append log file. On error REDIS_OK is returned. On non fatal
+/* Replay the append log file. On success REDIS_OK is returned. On non fatal
  * error (the append only file is zero-length) REDIS_ERR is returned. On
  * fatal error an error message is logged and the program exists. */
 int loadAppendOnlyFile(char *filename) {

src/rdb.c

@@ -474,7 +474,7 @@ int rdbLoadObjectType(rio *rdb) {
     return type;
 }
 
-/* Save a Redis object. Returns -1 on error, 0 on success. */
+/* Save a Redis object. Returns -1 on error, number of bytes written on success. */
 int rdbSaveObject(rio *rdb, robj *o) {
     int n, nwritten = 0;