swift234

Be more forgiving of implicit tuples with semi-valid source locations.

Previously, if we created an implicit tuple (i.e. no paren locations) and
exactly one of the first and last arguments had a valid location, we would
return an invalid SourceRange (one part valid, the other not). If we end
up in this situation (and the playground transform can) just return an
invalid range instead (as if the tuple were fully compiler-generated).

rdar://problem/19587250

Swift SVN r24703