Cancelling image picking causes Alert "Imgur upload failed" [fixes #628]

[felix-staud]

when opening the image picker in a new post or a new comment and then clicking cancel the error alert no long appears

PR Creator Checklist

Ensure you've checked the following before submitting your PR:

• You've discussed making your changes with a member of the dev team per contributing rules in the README
• Your changes are free of any lint errors
• Your changes are free of any typescript errors
• You've tested your changes

Summary

When opening the image picker in a new post or a new comment and then clicking cancel the error alert no long appears

Screenshots

Screen.Recording.2023-07-15.at.13.19.13.mov

Screen.Recording.2023-07-15.at.13.24.28.mov

Test Plan

New Post

1. Open lemmy app
2. Navigate to any community where you have a + Post Button available
3. Press the + Post Button
4. Click the image icon at the bottom right to open the img picker
5. Press Cancel at the top left
6. There should be NO alert anymore

New Comment

1. Open lemmy app
2. Open any Post where you can comment on
3. Press the +Comment Button
4. Click the image icon at the bottom right to open the img picker
5. Press Cancel at the top left
6. There should be NO alert anymore

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fixes #628