Fix is_optional flag propagation for selector schema

Author: mgreter

src/ast.cpp

@@ -1275,10 +1275,10 @@ namespace Sass {
       if ((*this)[i]->head()->is_empty_reference()) {
         // simply move to the next tail if we have "no" combinator
         if ((*this)[i]->combinator() == Complex_Selector::ANCESTOR_OF) {
-          if ((*this)[i]->tail() && (*this)[i]->has_line_feed()) {
-            (*this)[i]->tail()->has_line_feed(true);
-          }
           if ((*this)[i]->tail() != NULL) {
+            if ((*this)[i]->has_line_feed()) {
+              (*this)[i]->tail()->has_line_feed(true);
+            }
             (*this)[i] = (*this)[i]->tail();
           }
         }

src/eval.cpp

@@ -1683,6 +1683,7 @@ namespace Sass {
     std::vector<Selector_List*> rv;
     Selector_List* sl = SASS_MEMORY_NEW(ctx.mem, Selector_List, s->pstate());
     sl->media_block(s->media_block());
+    sl->is_optional(s->is_optional());
     for (size_t i = 0, iL = s->length(); i < iL; ++i) {
       rv.push_back(operator()((*s)[i]));
     }

src/expand.cpp

@@ -593,7 +593,7 @@ namespace Sass {
         error("Can't extend " + sel_str + ": can't extend nested selectors", c->pstate(), backtrace());
       }
       Compound_Selector* placeholder = c->head();
-      placeholder->is_optional(s->is_optional());
+      if (contextualized->is_optional()) placeholder->is_optional(true);
       for (size_t i = 0, L = extender->length(); i < L; ++i) {
         Complex_Selector* sel = (*extender)[i];
         if (!(sel->head() && sel->head()->length() > 0 &&