Opens a new chart with the specified symbol and period.
[in] Chart symbol. NULL means the symbol of the current chart (the Expert Advisor is attached to).
[in] Chart period (timeframe). Can be one of the ENUM_TIMEFRAMES values. 0 means the current chart period.
If successful, it returns the opened chart ID. Otherwise returns 0.
The maximum possible number of simultaneously open charts in the terminal can't exceed the CHARTS_MAX value.