`EmptyExpr` is somewhat unique, in that it's constructed in a circumstance
where the parser has been looking for a particular token or string of tokens
and has failed to find any. This means the parser state when constructing
`EmptyExpr` is fairly unique.
This gives rise to a bug where the parser constructs `EmptyExpr` with a
backwards span - a `start` value that's beyond the `end` value. This likely
happens because of the strange state the parser is in when recovering with
`EmptyExpr`.
This commit adds a backstop/workaround to avoid constructing such broken
`EmptyExpr` spans (or any other kind of span). Eventually, the parser state
should be fixed such that this does not occur, but that requires a
significant change to the parser's functionality, so a simple fix in th
interim is in order.
PR Close#41581
e1a2930893