Do not raise error from unknown channel id when parsing PSD layers

Tests/test_file_psd.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import io
 import sys
 import warnings
 
@@ -157,6 +158,21 @@ def test_no_icc_profile() -> None:
         assert "icc_profile" not in im.info
 
 
+def test_unknown_channel_id() -> None:
+    with open("Tests/images/rgba.psd", "rb") as fp:
+        data = fp.read()
+
+    # Set channel id to 4
+    data = data[:90] + b"\x00\x04" + data[92:]
+
+    b = io.BytesIO(data)
+    with Image.open(b) as im:
+        assert isinstance(im, PsdImagePlugin.PsdImageFile)
+
+        # unknown mode
+        assert im.layers[0][1] == ""
+
+
 def test_combined_larger_than_size() -> None:
     # The combined size of the individual parts is larger than the
     # declared 'size' of the extra data field, resulting in a backwards seek.

src/PIL/PsdImagePlugin.py

@@ -222,12 +222,14 @@ def read(size: int) -> bytes:
             continue
 
         for _ in range(ct_types):
-            type = i16(read(2))
+            channel_id = i16(read(2))
 
-            if type == 65535:
+            if channel_id == 65535:
                 b = "A"
+            elif channel_id < 4:
+                b = "RGBA"[channel_id]
             else:
-                b = "RGBA"[type]
+                b = ""
 
             bands.append(b)
             read(4)  # size