Merged in bugfix/export (pull request #2)

Fixed self.data check in file export

ui/main_window.py

@@ -222,7 +222,8 @@ class MainWindow(QMainWindow):
 
         file_format = file_format.lower()
 
-        if np.size(self.data, 0) < 3:
+        # Abort export if the #channels (rows in self.data) is 0
+        if np.size(self.data, 0) == 0:
             message = QMessageBox()
             QMessageBox.information(message, 'Saving data',
                                     'No data recorded yet', QMessageBox.Ok)