Add test for sampleformat corruption

Tests/test_file_tiff.py

@@ -587,6 +587,28 @@ class TestFileTiff(PillowTestCase):
             im.load()
             self.assertFalse(fp.closed)
 
+    def test_sampleformat_not_corrupted(self):
+        # Assert that a TIFF image with SampleFormat=UINT tag is not corrupted
+        # when saving to a new file.
+        # Pillow 6.0 fails with "OSError: cannot identify image file".
+        import base64
+        tiff = BytesIO(
+            base64.b64decode(
+                b'SUkqAAgAAAAPAP4ABAABAAAAAAAAAAABBAABAAAAAQAAAAEBBAABAAAAAQAA'
+                b'AAIBAwADAAAAwgAAAAMBAwABAAAACAAAAAYBAwABAAAAAgAAABEBBAABAAAA'
+                b'4AAAABUBAwABAAAAAwAAABYBBAABAAAAAQAAABcBBAABAAAACwAAABoBBQAB'
+                b'AAAAyAAAABsBBQABAAAA0AAAABwBAwABAAAAAQAAACgBAwABAAAAAQAAAFMB'
+                b'AwADAAAA2AAAAAAAAAAIAAgACAABAAAAAQAAAAEAAAABAAAAAQABAAEAAAB4'
+                b'nGNgYAAAAAMAAQ=='
+            )
+        )
+        out = BytesIO()
+        with Image.open(tiff) as im:
+            im.save(out, format='tiff')
+        out.seek(0)
+        with Image.open(out) as im:
+            im.load()
+
 
 @unittest.skipUnless(sys.platform.startswith("win32"), "Windows only")
 class TestFileTiffW32(PillowTestCase):