Ensure PNG seeks to end of previous chunk at start of load_end

Tests/test_file_png.py

@@ -628,6 +628,23 @@ def test_textual_chunks_after_idat(self):
         with Image.open("Tests/images/hopper_idat_after_image_end.png") as im:
             assert im.text == {"TXT": "VALUE", "ZIP": "VALUE"}
 
+    def test_padded_idat(self):
+        # This image has been manually hexedited
+        # so that the IDAT chunk has padding at the end
+        # Set MAXBLOCK to the length of the actual data
+        # so that the decoder finishes reading before the chunk ends
+        MAXBLOCK = ImageFile.MAXBLOCK
+        ImageFile.MAXBLOCK = 45
+        ImageFile.LOAD_TRUNCATED_IMAGES = True
+
+        with Image.open("Tests/images/padded_idat.png") as im:
+            im.load()
+
+            ImageFile.MAXBLOCK = MAXBLOCK
+            ImageFile.LOAD_TRUNCATED_IMAGES = False
+
+            assert_image_equal_tofile(im, "Tests/images/bw_gradient.png")
+
     def test_specify_bits(self, tmp_path):
         im = hopper("P")
 

src/PIL/PngImagePlugin.py

@@ -920,6 +920,8 @@ def load_read(self, read_bytes):
 
     def load_end(self):
         """internal: finished reading image data"""
+        if self.__idat != 0:
+            self.fp.read(self.__idat)
         while True:
             self.fp.read(4)  # CRC