Fixed MetaLinePlotterIndicator

The indicator should not derive its lines from cls but should derive them from proto lines. This fixes using more than one line plotter indicator. After the first indicator, indicators contain lines from previous indicators.

Author: happydasch

backtrader/indicator.py

@@ -141,8 +141,7 @@ def donew(cls, *args, **kwargs):
         lname = kwargs.pop('name')
         name = cls.__name__
 
-        lines = getattr(cls, 'lines', Lines)
-        cls.lines = lines._derive(name, (lname,), 0, [])
+        cls.lines = Lines._derive(name, (lname,), 0, [])
 
         plotlines = AutoInfoClass
         newplotlines = dict()