Minor perf tests framework improvement

modules/ts/include/opencv2/ts/ts_perf.hpp

@@ -287,7 +287,7 @@ private:
 
         _declareHelper& iterations(int n);
         _declareHelper& time(double timeLimitSecs);
-        _declareHelper& tbb_threads(int n);
+        _declareHelper& tbb_threads(int n = -1);
     private:
         TestBase* test;
         _declareHelper(TestBase* t);

modules/ts/src/ts_perf.cpp

@@ -898,10 +898,9 @@ TestBase::_declareHelper& TestBase::_declareHelper::time(double timeLimitSecs)
 TestBase::_declareHelper& TestBase::_declareHelper::tbb_threads(int n)
 {
 #ifdef HAVE_TBB
-    if (n > 0) {
     test->p_tbb_initializer.release();
+    if (n > 0)
         test->p_tbb_initializer=new tbb::task_scheduler_init(n);
-    }
 #endif
     return *this;
 }