fix slice in sar head

ppocr/modeling/heads/rec_sar_head.py

@@ -235,6 +235,7 @@ class ParallelSARDecoder(BaseDecoder):
             # cal mask of attention weight
             for i, valid_ratio in enumerate(valid_ratios):
                 valid_width = min(w, math.ceil(w * valid_ratio))
+                if valid_width < w:
                     attn_weight[i, :, :, valid_width:, :] = float('-inf')
 
         attn_weight = paddle.reshape(attn_weight, [bsz, T, -1])