MdePkg: Check input Ptrs in GetSectionFromAnyFvByFileType

MdePkg: Check input Ptrs in GetSectionFromAnyFvByFileType

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1337

In function GetSectionFromAnyFvByFileType, the input parameter "Buffer"
and "size" should not be NULL, so add ASSERT here to avoid any checker
report that the NULL pointer may be used.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>