[WinEH] Skip state numbering when no EH pads are present

[WinEH] Skip state numbering when no EH pads are present

Otherwise we'd try to emit the thunk that passes the LSDA to
__CxxFrameHandler3. We don't emit the LSDA if there were no landingpads,
so we'd end up with an assembler error when trying to write the COFF
object.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247820 91177308-0d34-0410-b5e6-96231b3b80d8