Fix a bug in the DXE Core that generates an ASSERT() when the page at address zero...

Fix a bug in the DXE Core that generates an ASSERT() when the page at address zero is freed and DEBUG_CLEAR_MEMORY() macros are enabled.  If DEBUG_CLEAR_MEMORY() is enabled and the page at address 0 is freed, then DEBUG_CLEAR_MEMORY() is invoked skipping over the first 4K page.

Signed-off-by: Michael Kinney <michael.d.kinney@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@14217 6f19259b-4bc3-4df7-8a09-765794883524