SEH handler gets installed after DLLMain() call

[BigJim]

The optional SEH handler local implementation of RtlInsertInvertedFunctionTable() is called after the DLLMain() gets called in LdrMapDllMemory.

If an exception happens in DLLMain() it won't be caught (and thus becomes "unhandled").

It would be better to have the exception handler be installed before DLLMain() and is default behavior for the OS too.