Fix issue where the unsigned value used for the the map select budget could underflow

Fix issue where the unsigned value used for the the map select budget could underflow
resulting in an unlimited budget

Changed m_mapSelectBudget and budget to be a signed integer
Added an assert that ensures that the remaining budget is between [0..m_mapSelectBudget]
Change the test for running out of budge to be a <= zero test instead of an equal zero test.

Fixed the bug in the handling of phiArgs in VNForMapSelectWork
by adding a check if we exceeded our budget when processing the first phiArg.

Added a define for DEFAULT_MAP_SELECT_BUDGET