BUG: n_frames is incorrect

[WuZifan]

What did you do?

i try to load every frame of a gif by the following code

# PILLOW==9.1.0

img = Image.open('./test.gif')
for I in range(img.n_frames):
    tmp.seek(i)

below is the test img and I find that img.n_frames gives me 2 but the actual frame number is 1,so the seek function raise an EOF error.

What did you expect to happen?

load all the frame without any error

What actually happened?

The following error is raised.
raise EOFError("no more images in GIF file") from e

What are your OS, Python and Pillow versions?

• OS: macos m1
• Python: 3.7.0
• Pillow: 9.1.0

from PIL import Image
img = Image.open('./test.gif')
for I in range(img.n_frames):
    tmp.seek(i)

[radarhere]

Testing, I find that #6219 will resolve this.