ykpiv: when decoding an object compare lengths correctly

the length comparison when reading an object out was messed up, this
fixes it to compare correctly.

relates #154

lib/ykpiv.c

@@ -1282,7 +1282,7 @@ ykpiv_rc _ykpiv_fetch_object(ykpiv_state *state, int object_id,
     if(offs == 0) {
       return YKPIV_SIZE_ERROR;
     }
-    if(outlen > offs + 1 + *len) {
+    if(outlen + offs + 1 != *len) {
       if(state->verbose) {
         fprintf(stderr, "Invalid length indicated in object, total objlen is %lu, indicated length is %lu.", *len, outlen);
       }