Restore original encoderinfo after saving (#8942)

Author: hugovk

Tests/test_file_mpo.py

@@ -318,6 +318,9 @@ def test_save_xmp() -> None:
     im2.encoderinfo = {"xmp": b"Second frame"}
     im_reloaded = roundtrip(im, xmp=b"First frame", save_all=True, append_images=[im2])
 
+    # Test that encoderinfo is unchanged
+    assert im2.encoderinfo == {"xmp": b"Second frame"}
+
     assert im_reloaded.info["xmp"] == b"First frame"
 
     im_reloaded.seek(1)

src/PIL/Image.py

@@ -2556,7 +2556,8 @@ def save(
             self.load()
 
         save_all = params.pop("save_all", None)
-        self.encoderinfo = {**getattr(self, "encoderinfo", {}), **params}
+        encoderinfo = getattr(self, "encoderinfo", {})
+        self.encoderinfo = {**encoderinfo, **params}
         self.encoderconfig: tuple[Any, ...] = ()
 
         if format.upper() not in SAVE:
@@ -2594,10 +2595,7 @@ def save(
                     pass
             raise
         finally:
-            try:
-                del self.encoderinfo
-            except AttributeError:
-                pass
+            self.encoderinfo = encoderinfo
         if open_fp:
             fp.close()