Allow for APP1 markers without EXIF data

Tests/test_file_mpo.py

@@ -91,6 +91,18 @@ def test_exif(test_file: str) -> None:
         assert info[34665] == 188
 
 
+def test_app1_not_exif() -> None:
+    with open("Tests/images/sugarshack.mpo", "rb") as fp:
+        data = fp.read()
+    data = data[:60014] + b" " + data[60015:]
+    b = BytesIO(data)
+    with Image.open(b) as im:
+        del im.info["exif"]
+
+        im.seek(1)
+        assert "exif" not in im.info
+
+
 def test_frame_size() -> None:
     # This image has been hexedited to contain a different size
     # in the EXIF data of the second frame

src/PIL/MpoImagePlugin.py

@@ -145,14 +145,16 @@ def seek(self, frame):
         self._size = self._initial_size
         if i16(segment) == 0xFFE1:  # APP1
             n = i16(self.fp.read(2)) - 2
-            self.info["exif"] = ImageFile._safe_read(self.fp, n)
-            self._reload_exif()
-
-            mptype = self.mpinfo[0xB002][frame]["Attribute"]["MPType"]
-            if mptype.startswith("Large Thumbnail"):
-                exif = self.getexif().get_ifd(ExifTags.IFD.Exif)
-                if 40962 in exif and 40963 in exif:
-                    self._size = (exif[40962], exif[40963])
+            s = ImageFile._safe_read(self.fp, n)
+            if s[:6] == b"Exif\0\0":
+                self.info["exif"] = s
+                self._reload_exif()
+
+                mptype = self.mpinfo[0xB002][frame]["Attribute"]["MPType"]
+                if mptype.startswith("Large Thumbnail"):
+                    exif = self.getexif().get_ifd(ExifTags.IFD.Exif)
+                    if 40962 in exif and 40963 in exif:
+                        self._size = (exif[40962], exif[40963])
         elif "exif" in self.info:
             del self.info["exif"]
             self._reload_exif()