Fixed sdscat*() bug: read memory error

Author: iiol

sds.c

@@ -399,7 +399,7 @@ sds sdscatlen(sds s, const void *t, size_t len) {
 
     s = sdsMakeRoomFor(s,len);
     if (s == NULL) return NULL;
-    memcpy(s+curlen, t, len);
+    memmove(s+curlen, t, len);
     sdssetlen(s, curlen+len);
     s[curlen+len] = '\0';
     return s;