Add samples number check in data callback (SCAN-522)

src/BufferedAcquisition.cpp

@@ -216,6 +216,16 @@ throw (ni660Xsl::DAQException)
 void BufferedAcquisition::get_scaled_buffer(void) 
 throw (ni660Xsl::DAQException)
 {
+	// check samples number > 0
+	if (this->nb_samples_ == 0)
+	{
+	  this->state_ = UNKNOWN;
+	  throw ni660Xsl::DAQException("reading data failed",
+			"internal error - samples number failed to null value",
+			"BufferedAcquisition::get_scaled_buffer",
+			-1);
+	}
+
 	ni660Xsl::InScaledBuffer* sb = new ni660Xsl::InScaledBuffer(this->nb_samples_);
 	long _samples_read;
     int err = DAQmxReadCounterF64(this->task_handle_, this->nb_samples_, this->timeout_,