[parser] Clear scope for inner block in function with complex parameters

The parser was finalizing the inner block scope, but not clearing the
inner block's scope pointer. This doesn't (yet) have any behavioral
difference, but makes it easier to make assumptions about the structure
of the AST vs the scope chain.

R=neis@chromium.org

Review-Url: https://codereview.chromium.org/2696233003
Cr-Commit-Position: refs/heads/master@{#43233}

src/parsing/parser-base.h

@@ -4045,6 +4045,8 @@ void ParserBase<Impl>::ParseFunctionBody(
     if (inner_scope->FinalizeBlockScope() != nullptr) {
       impl()->CheckConflictingVarDeclarations(inner_scope, CHECK_OK_VOID);
       impl()->InsertShadowingVarBindingInitializers(inner_block);
+    } else {
+      inner_block->set_scope(nullptr);
     }
     inner_scope = nullptr;