[Annotations] "Error saving edited shot" dialog is displayed when you try to save a very large edited shot

[SoftVision-CosminMuntean]

[Notes]:

• Also, after you dismiss the dialog, you get another one: "Connection error".

[Affected versions]:

• Nightly 59.0a1
• Screenshots 28.0.0 dev

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• The "xpinstall.signatures.required" boolean pref is set to "false".
• The "extensions.legacy.enabled" boolean pref is set tot "true".
• Have the Screenshots 28.0.0 dev version installed from here, on a new clean profile.

[Steps to reproduce]:

1. Open latest Nightly build with the profile from prerequisites and navigate to a large website (eg. imgur.com).
2. Scroll the page to load more content and from the "Page Actions" menu choose the "Take a Screenshot" option.
3. Click the "Save full page" button from the top right corner of the page.
4. Click the "Edit this shot" button.
5. Draw something on the shot and click the "Save" button.
6. Observe the behavior.

[Expected result]:

• The changes are successfully saved.

[Actual result]:

• "Error saving edited shot" dialog is displayed and the changes are not saved.

[Additional Notes]:

• Here is a screen recording with the issue: