driver-ztex: only reset errors if there are some

Only check the errors and print the log message if
there actually were errros.

driver-ztex.c

@@ -327,12 +327,14 @@ static int64_t ztex_scanhash(struct thr_info *thr, struct work *work,
 
 	// only add the errorCount if we had at least some valid nonces or
 	// had no valid nonces in the last round
+	if (errorCount > 0.0) {
 		if (ztex->nonceCheckValid > 0 && validNonces == 0) {
 			applog(LOG_ERR, "%s: resetting %.1f errors", ztex->repr, errorCount);
 		}
 		else {
 			ztex->errorCount[ztex->freqM] += errorCount;
 		}
+	}
 
 	// remember the number of valid nonces for the check in the next round
 	ztex->nonceCheckValid = validNonces;