Area for storage exfiltration

[NandanaPerera]

Bank area contributing to storage infiltration in exfil_getLoss (exfil.c) is computed by:
area = MIN(area, exfil->bankMaxArea) - exfil->btmArea;

This seems to be assuming storage area is continuously increasing (similar to storage pond). For a storage curve that has a maximum area in the middle (such as an underground chamber as below - this also has gravel layers at the bottom and top with reduced area from porosity), infiltrating bank area above the bankMaxDepth should consider the bankMaxArea.