Selector: Make selectors with leading combinators use qSA again

Selector: Make selectors with leading combinators use qSA again

An optimization added in jquery/sizzle#431 skips the temporary IDs for selectors
not using child or descendant combinators. For sibling combinators, though, this
pushes a selector with a leading combinator to qSA directly which crashes and
falls back to a slower Sizzle route.

This commit makes selectors with leading combinators not skip the selector
rewriting. Note that after jquery/jquery#4454 & jquery/sizzle#453, all modern
browsers other than Edge leverage the :scope pseudo-class, avoiding temporary
id attributes.

Closes gh-4509
Ref jquery/sizzle#431