ShellPkg: Add checks for NULL pointers.

This adds lots of pointer verification with ASSERTs only used when the condition should be impossible and never for memory allocation.

signed-off-by: jcarsey
reviewed-by: geekboy15a

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@12523 6f19259b-4bc3-4df7-8a09-765794883524

ShellPkg/Library/UefiShellDebug1CommandsLib/HexEdit/FileImage.c

@@ -169,7 +169,7 @@ HFileImageRead (
   // you should set the status string
   //
   Status = ReadFileIntoBuffer (FileName, (VOID**)&Buffer, &HFileImage.Size, &HFileImage.ReadOnly);
-  if (EFI_ERROR(Status)) {
+  if (EFI_ERROR(Status) || Buffer == NULL) {
     UnicodeBuffer = CatSPrint(NULL, L"Read error on file &s: %r", FileName, Status);
     if (UnicodeBuffer == NULL) {
       SHELL_FREE_NON_NULL(Buffer);