fix loader cause it does not need to break (#2562)

* fix loader cause it does not need to be rebuild for each epoch

* fix loader for dynamic sample

* rm thin import

ppocr/utils/e2e_utils/extract_textpoint_fast.py

@@ -21,7 +21,6 @@ import math
 
 import numpy as np
 from itertools import groupby
-from cv2.ximgproc import thinning as thin
 from skimage.morphology._skeletonize import thin
 
 

tools/program.py

@@ -196,10 +196,8 @@ def train(config,
         train_reader_cost = 0.0
         batch_sum = 0
         batch_start = time.time()
-        for idx, batch in enumerate(train_dataloader):
+        for idx, batch in enumerate(train_dataloader()):
             train_reader_cost += time.time() - batch_start
-            if idx >= len(train_dataloader):
-                break
             lr = optimizer.get_lr()
             images = batch[0]
             if use_srn: