Ensure enough data available while disassembling

src/iw5/stdafx.hpp

@@ -31,6 +31,7 @@
 #include <fstream>
 #include <unordered_map>
 #include <stdio.h>
+#include <cassert>
 
 // Ext
 using namespace std::literals;

src/iw5/xsk/disassembler.cpp

@@ -71,6 +71,7 @@ void disassembler::dissasemble_function(const gsc::function_ptr& func)
         func->instructions.push_back(std::make_unique<gsc::instruction>());
         auto& inst = func->instructions.back();
         inst->index = static_cast<std::uint32_t>(script_->pos());
+        assert(script_->is_avail());
         inst->opcode = script_->read<std::uint8_t>();
         inst->size = opcode_size(inst->opcode);