ShellPkg: Remove ASSERT

ShellPkg: Remove ASSERT

This change removes ASSERT statements and replaces them with logic to break out of the loop.  This both prevents spinning forever and prevents processing the returned data from the function that failed.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15133 6f19259b-4bc3-4df7-8a09-765794883524