[C++] Fix a CHECK failure

Stats::Start could be recursively called. Also, measuring
evaluation time of $(wildcard) parameters didn't make sense.
diff --git a/func.cc b/func.cc
index 34fca3e..dfa9a71 100644
--- a/func.cc
+++ b/func.cc
@@ -305,8 +305,8 @@
 }
 
 void WildcardFunc(const vector<Value*>& args, Evaluator* ev, string* s) {
-  COLLECT_STATS("func wildcard time");
   const string&& pat = args[0]->Eval(ev);
+  COLLECT_STATS("func wildcard time");
   // Note GNU make does not delay the execution of $(wildcard) so we
   // do not need to check avoid_io here.
   WordWriter ww(s);