Bug: lisflood model class: model start time

[SarahAlidoost]

Lisflood returns None for the first two days: for example if forcing start date is '1990-01-01', discharge values are None for '1990-01-01' and '1990-01-02'. Either this line in the class implementation or the lisflood bmi model causes this problem! The issue can be investigated using lisflood_testrun_notebook.