fixed the bug: local variable 't4' referenced before assignment

qurator/sbb_textline_detector/main.py

@@ -1460,6 +1460,7 @@ class textlineerkenner:
         print( "time total = "+"{0:.2f}".format(time.time()-t1) )
         print( "time needed for page extraction = "+"{0:.2f}".format(t2-t1) )
         print( "time needed for text region extraction and get contours = "+"{0:.2f}".format(t3-t2) )
+        if len(contours)>0:
             print( "time needed for textlines = "+"{0:.2f}".format(t4-t3) )
             print( "time needed to get slopes of regions (deskewing) = "+"{0:.2f}".format(t5-t4) )
             print( "time needed to get order of regions = "+"{0:.2f}".format(t6-t5) )