MdePkg DxeServicesLib: Handle potential NULL FvHandle
MdePkg DxeServicesLib: Handle potential NULL FvHandle

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=514

The FvHandle input to InternalGetSectionFromFv() may be NULL,
then ASSERT will appear. It is because the LoadedImage->DeviceHandle
returned from InternalImageHandleToFvHandle() may be NULL.
For example for DxeCore, there is LoadedImage protocol installed
for it, but the LoadedImage->DeviceHandle could not be initialized
before the FV2 (contain DxeCore) protocol is installed.

This patch is to update InternalGetSectionFromFv() to return
EFI_NOT_FOUND directly for NULL FvHandle.

Cc: Liming Gao <6480311aeeb4b006862f6d13ebabddc03f51e507@intel.com>
Cc: Michael Kinney <fd20bc543a9f65bb633fac7d08a403c1f1c8eb6c@intel.com>
Cc: Michael Turner <11395a38e83f51272ca943e4e2bc4038e7ccbae2@microsoft.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <5c6bb72efe464613af94e84c05522a361b23844a@intel.com>
Reviewed-by: Liming Gao <6480311aeeb4b006862f6d13ebabddc03f51e507@intel.com>

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