Don't build RTrees if test results will be ignored.

pcbnew/drc/drc_test_provider_silk_clearance.cpp

@@ -87,6 +87,12 @@ bool DRC_TEST_PROVIDER_SILK_CLEARANCE::Run()
     DRC_CONSTRAINT worstClearanceConstraint;
     m_largestClearance = 0;
 
+    if( m_drcEngine->IsErrorLimitExceeded( DRCE_OVERLAPPING_SILK ) )
+    {
+        reportAux( "Silkscreen clearance testing not run." );
+        return false;
+    }
+
     if( m_drcEngine->QueryWorstConstraint( DRC_CONSTRAINT_TYPE_SILK_CLEARANCE,
                                            worstClearanceConstraint, DRCCQ_LARGEST_MINIMUM ) )
     {

pcbnew/drc/drc_test_provider_silk_to_mask.cpp

@@ -84,6 +84,12 @@ bool DRC_TEST_PROVIDER_SILK_TO_MASK::Run()
 {
     m_board = m_drcEngine->GetBoard();
 
+    if( m_drcEngine->IsErrorLimitExceeded( DRCE_SILK_MASK_CLEARANCE ) )
+    {
+        reportAux( "Silkscreen clipping tests not run." );
+        return false;
+    }
+
     DRC_CONSTRAINT worstClearanceConstraint;
     m_largestClearance = 0;