Raise mode error before reading

Author: radarhere

Tests/test_imagefontpil.py

@@ -30,6 +30,14 @@ def test_default_font(font: ImageFont.ImageFont) -> None:
     assert_image_equal_tofile(im, "Tests/images/default_font.png")
 
 
+def test_invalid_mode() -> None:
+    font = ImageFont.ImageFont()
+    fp = BytesIO()
+    with Image.open("Tests/images/hopper.png") as im:
+        with pytest.raises(TypeError, match="invalid font image mode"):
+            font._load_pilfont_data(fp, im)
+
+
 def test_without_freetype() -> None:
     original_core = ImageFont.core
     if features.check_module("freetype2"):

src/PIL/ImageFont.py

@@ -125,6 +125,11 @@ def _load_pilfont(self, filename: str) -> None:
             image.close()
 
     def _load_pilfont_data(self, file: IO[bytes], image: Image.Image) -> None:
+        # check image
+        if image.mode not in ("1", "L"):
+            msg = "invalid font image mode"
+            raise TypeError(msg)
+
         # read PILfont header
         if file.read(8) != b"PILfont\n":
             msg = "Not a PILfont file"
@@ -140,11 +145,6 @@ def _load_pilfont_data(self, file: IO[bytes], image: Image.Image) -> None:
         # read PILfont metrics
         data = file.read(256 * 20)
 
-        # check image
-        if image.mode not in ("1", "L"):
-            msg = "invalid font image mode"
-            raise TypeError(msg)
-
         image.load()
 
         self.font = Image.core.font(image.im, data)