calc_profit() TypeError: unsupported operand type(s) for *: 'float' and 'NoneType'

[bitphage]

From #563

Traceback (most recent call last):
File "/home/cryptokong/.local/lib/python3.6/site-packages/dexbot-0.10.1-py3.6.egg/dexbot/worker.py", line 76, in init_workers
view=self.view
File "/home/cryptokong/.local/lib/python3.6/site-packages/dexbot-0.10.1-py3.6.egg/dexbot/strategies/staggered_orders.py", line 115, in init
self.update_gui_profit()
File "/home/cryptokong/.local/lib/python3.6/site-packages/dexbot-0.10.1-py3.6.egg/dexbot/strategies/base.py", line 1390, in update_gui_profit
profit = self.calc_profit()
File "/home/cryptokong/.local/lib/python3.6/site-packages/dexbot-0.10.1-py3.6.egg/dexbot/strategies/base.py", line 1167, in calc_profit
max_quantity_base = base_balance + quote_balance * center_price
TypeError: unsupported operand type(s) for *: 'float' and 'NoneType'

The problem caused by the error in conditional expression if not (old_center_price or center_price)