process error should not cause parse error

Author: mishanga

lib/csscomb.js

@@ -85,10 +85,11 @@ Comb.prototype = {
     processString: function(text, filename) {
         var tree;
         try {
-            tree = this.processTree(cssp.parse(text));
+            tree = cssp.parse(text);
         } catch (e) {
             throw new Error('Parsing error at ' + filename + ': ' + e.message);
         }
+        tree = this.processTree(tree);
         return cssp.translate(tree);
     },