compiler: don't advance past unexpected semicolon
compiler: don't advance past unexpected semicolon

We've already read the unexpected semicolon, so advancing again causes
us to skip the next token, causing future errors to be out of sync.

Change-Id: Id83776a31996dbfd4734420fd3e8b4cfcc14d2f0
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/274439
Trust: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Reviewed-by: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>

golang/gofrontend,golang/gofrontend,golang/gofrontend,golang/gofrontend