Frontend: End multiblocks early after hitting 2 consecutive null bytes

'add [rax], al' is almost never seen in actual code so the assumption
can be made that we are most likely trying to explore garbage code and
that this will never be hit. If it is then code will be generated at
that point (where Entrypoint == true).

FEXCore/Source/Interface/Core/Frontend.cpp

@@ -1103,6 +1103,12 @@ void Decoder::DecodeInstructionsAtEntry(const uint8_t* _InstStream, uint64_t PC,
       auto OpMinPage = OpMinAddress & FEXCore::Utils::FEX_PAGE_MASK;
       auto OpMaxPage = OpMaxAddress & FEXCore::Utils::FEX_PAGE_MASK;
 
+      if (!EntryBlock && OpMinPage == OpMaxPage && PeekByte(0) == 0 && PeekByte(1) == 0) [[unlikely]] {
+        // End the multiblock early if we hit 2 consecutive null bytes (add [rax], al) in the same page with the
+        // assumption we are most likely trying to explore garbage code.
+        break;
+      }
+
       if (OpMinPage != CurrentCodePage) {
         CurrentCodePage = OpMinPage;
         CodePages.insert(CurrentCodePage);