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#4454 & jquery/sizzle#453, all modern
browsers other than Edge leverage the :scope pseudo-class, avoiding temporary
id attributes.

Ref jquerygh-4509
Ref jquery/sizzle#431

src/selector.js

@@ -242,8 +242,11 @@ function find( selector, context, results, seed ) {
 				// descendant combinators, which is not what we want.
 				// In such cases, we work around the behavior by prefixing every selector in the
 				// list with an ID selector referencing the scope context.
+				// The technique has to be used as well when a leading combinator is used
+				// as such selectors are not recognized by querySelectorAll.
 				// Thanks to Andrew Dupont for this technique.
-				if ( nodeType === 1 && rdescend.test( selector ) ) {
+				if ( nodeType === 1 &&
+					( rdescend.test( selector ) || rcombinators.test( selector ) ) ) {
 
 					// Expand context for sibling selectors
 					newContext = rsibling.test( selector ) && testContext( context.parentNode ) ||