Considering keep track of the index of global table

[qtiuto <qtiuto@...>]

While lua_load will always set the first upvalue of a dumped function to the global table, the actual index of the global table is related to the first time it's used in the function.If some local value is used
first,then its upvalue index will be lower than _ENV.
What's worse,if I use strip mode, I can't figure out the actual index of the _ENV when I load it.So, it would  better add one more int in dumped content to keep track of the global index and when load it, set its value to global table,rather than trying to figure out whether it has one more upvalue after undump, and setting the first value to the global value.It will cause a bug!

The fix is little.However, I don't want to type it in my phone