Fix panning of zoomed images

[starypatyk]

When an image is enlarged (zoomed using the scroll wheel), panning (dragging) behaves incorrectly:

• It is not possible to see parts of the image close to the border.
• The image does not "catch" with the dragging - it feels like the image resists dragging.

I see that there is an open PR #1063 that is broader in scope and apparently fixes this issue as well. However it did not progress for over a year now. 😞

In this PR, I propose a very small, alternative change that should fix just the two issues mentioned above.

If you think it is better to continue with #1063, I can try to pick it up instead.

Full image:

Before
Zoomed image dragged down as much as possible - row 0 is not visible

After
Zoomed image dragged down as much as possible - row 0 is visible

[skjnldsv]

wow, that looks like a nice typo! Can't believe that hasn't been caught in all those years

[starypatyk]

The key issue was incorrect calculation of top/left margins. I must admit that I am not fluent enough in CSS to fully understand why the shift must be multiplied by 2 to get the margins correct. But observations of the calculated box model in dev tools and testing confirmed this is the case. 😇

[skjnldsv]

/backport to stable27

[skjnldsv]

/backport to stable26

[backportbot-nextcloud]

The backport to stable27 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable27
git pull origin stable27

# Create the new backport branch
git checkout -b fix/foo-stable27

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable27

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

[backportbot-nextcloud]

The backport to stable26 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable26
git pull origin stable26

# Create the new backport branch
git checkout -b fix/foo-stable26

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable26

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

[skjnldsv]

/backport to stable27

[skjnldsv]

/backport to stable26

[backportbot-nextcloud]

The backport to stable27 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable27
git pull origin stable27

# Create the new backport branch
git checkout -b fix/foo-stable27

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable27

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

[backportbot-nextcloud]

The backport to stable26 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable26
git pull origin stable26

# Create the new backport branch
git checkout -b fix/foo-stable26

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable26

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

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