fixing the selector lookahead to guard against missing/empty selectors

Author: Aaron Leung

parser.cpp

@@ -1469,6 +1469,7 @@ namespace Sass {
   {
     const char* p = start ? start : position;
     const char* q;
+    bool saw_stuff = false;
     bool saw_interpolant = false;
 
     while ((q = peek< identifier >(p))                             ||
@@ -1508,12 +1509,13 @@ namespace Sass {
            (q = peek< sequence< exactly<'-'>, interpolant > >(p))  ||
            (q = peek< sequence< pseudo_prefix, interpolant > >(p)) ||
            (q = peek< interpolant >(p))) {
+      saw_stuff = true;
       p = q;
       if (*(p - 1) == '}') saw_interpolant = true;
     }
 
     Selector_Lookahead result;
-    result.found            = peek< exactly<'{'> >(p) ? p : 0;
+    result.found            = saw_stuff && peek< exactly<'{'> >(p) ? p : 0;
     result.has_interpolants = saw_interpolant;
 
     return result;