MdeModulePkg/UdfDxe: Add checks to ensure no possible NULL ptr deref

MdeModulePkg/UdfDxe: Add checks to ensure no possible NULL ptr deref

Case 1 - Within DuplicateFid() & DuplicateFe():
The call to AllocateCopyPool() may return NULL.
Add ASSERTs as checks.

Case 2 - Within UdfRead():
Add ASSERT to ensure 'NewFileEntryData' returned from FindFileEntry()
will not be NULL pointer.

Case 3 - Within GetAllocationDescriptorLsn():
The return value of 'GetPdFromLongAd (Volume, ParentIcb)' may be NULL,
and it will be passed into function GetShortAdLsn() which will
dereference it.
Add ASSERT in GetShortAdLsn() as check.

Case 4 - Within ReadFile():
Add ASSERT to ensure 'Data' returned from GetAedAdsData() will not be NULL
pointer.

Case 5 - Within InternalFindFile():
If both 'Parent->FileIdentifierDesc' and 'Icb' are NULL, then possible
NULL pointer dereference will happen in ReadDirectoryEntry().
Add additional check to resolve.

Cc: Paulo Alcantara <pcacjr@zytor.com>
Cc: Ruiyu Ni <ruiyu.ni@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: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Paulo Alcantara <pcacjr@zytor.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>