Add extra debugging details for Mixin_Call

Author: xzyfer

src/ast.hpp

@@ -389,7 +389,7 @@ namespace Sass {
     { }
     virtual bool has_content()
     {
-      return block_->has_content() || Statement::has_content();
+      return (block_ && block_->has_content()) || Statement::has_content();
     }
     virtual ~Has_Block() = 0;
   };

src/debugger.hpp

@@ -386,7 +386,8 @@ inline void debug_ast(AST_Node* node, std::string ind, Env* env)
   } else if (dynamic_cast<Mixin_Call*>(node)) {
     Mixin_Call* block = dynamic_cast<Mixin_Call*>(node);
     std::cerr << ind << "Mixin_Call " << block << " " << block->tabs();
-    std::cerr << " [" <<  block->name() << "]" << std::endl;
+    std::cerr << " [" <<  block->name() << "]";
+    std::cerr << " [has_content: " << block->has_content() << "] " << std::endl;
     debug_ast(block->arguments(), ind + " args: ");
     if (block->block()) for(auto i : block->block()->elements()) { debug_ast(i, ind + " ", env); }
   } else if (Ruleset* ruleset = dynamic_cast<Ruleset*>(node)) {