MdeModulePkg/Core: Fix potential array overflow

MdeModulePkg/Core: Fix potential array overflow

In the method DumpGuardedMemoryBitmap() and SetAllGuardPages(), the code
didn't check if the global mMapLevel is legal value or not, which leaves
a logic hole causing potential array overflow in code followed.

This patch adds sanity check before any array reference in those methods.

Cc: Wu Hao <hao.a.wu@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Wu Hao <hao.a.wu@intel.com>