Handle EXIF data truncated to just the header

Tests/test_image.py

@@ -666,6 +666,19 @@ class TestImage:
 
             assert not fp.closed
 
+    def test_empty_exif(self):
+        with Image.open("Tests/images/exif.png") as im:
+            exif = im.getexif()
+        assert dict(exif) != {}
+
+        # Test that exif data is cleared after another load
+        exif.load(None)
+        assert dict(exif) == {}
+
+        # Test loading just the EXIF header
+        exif.load(b"Exif\x00\x00")
+        assert dict(exif) == {}
+
     @mark_if_feature_version(
         pytest.mark.valgrind_known_error, "libjpeg_turbo", "2.0", reason="Known Failing"
     )

src/PIL/Image.py

@@ -3478,12 +3478,12 @@ class Exif(MutableMapping):
         self._loaded_exif = data
         self._data.clear()
         self._ifds.clear()
+        if data and data.startswith(b"Exif\x00\x00"):
+            data = data[6:]
         if not data:
             self._info = None
             return
 
-        if data.startswith(b"Exif\x00\x00"):
-            data = data[6:]
         self.fp = io.BytesIO(data)
         self.head = self.fp.read(8)
         # process dictionary