Fix png image plugin load_end func handle truncated file.

Author: lajiyuan

Tests/images/end_trunc_file.png

@@ -777,6 +777,15 @@ class MyStdOut:
             mystdout = mystdout.buffer
         with Image.open(mystdout) as reloaded:
             assert_image_equal_tofile(reloaded, TEST_PNG_FILE)
+    
+    def test_end_truncated_file(self):
+        ImageFile.LOAD_TRUNCATED_IMAGES = True
+        try:
+            with Image.open("Tests/images/end_trunc_file.png") as im:
+                assert_image_equal_tofile(im, "Tests/images/end_trunc_file.png")
+        finally:
+            ImageFile.LOAD_TRUNCATED_IMAGES = False
+
 
 
 @pytest.mark.skipif(is_win32(), reason="Requires Unix or macOS")

Tests/test_file_png.py

@@ -981,7 +981,13 @@ def load_end(self):
             except EOFError:
                 if cid == b"fdAT":
                     length -= 4
-                ImageFile._safe_read(self.fp, length)
+                try:
+                    ImageFile._safe_read(self.fp, length)
+                except OSError as e:
+                    if ImageFile.LOAD_TRUNCATED_IMAGES:
+                        break
+                    else:
+                        raise e
             except AttributeError:
                 logger.debug("%r %s %s (unknown)", cid, pos, length)
                 s = ImageFile._safe_read(self.fp, length)