Canvas size not automatically recalculated when changed by Paste Embedded

[SjoerdV]

Describe the bug
If one pastes an embedded image (2) with larger dimensions than the image (1) it is pasted in, the canvas of (1) does not automatically expand in memory (it does on screen!).
Operations like Crop or other Image effects will not use the updated larger canvas size, but apply their operations to the original canvas size, even after Save. One really has top full close the image and reopen it, for further editing to succeed

To Reproduce
Steps to reproduce the behavior:

1. Make a small screenshot (Rectangular image) (1)
2. Make a full screen screenshot (2)
3. Paste Embedded (2) inside (1) -> canvas will expand visually
4. Save (1)
5. Click on Effects / Drop Shadow OR Crop for (1)
6. Wrong (original) canvas size is being changed

Expected behavior
When an effect is added or crop is initiated the updated canvas size should be used.

Screenshots

Desktop (please complete the following information):

• OS: Linux
• Distribution in case of Linux [e.g. Ubuntu]: Mint
• Window System in case of Linux [e.g. X11]: X11
• ksnip version [e.g. 1.8.0]: 1.10.0
• How did you install ksnip [e.g. AppImage]: deb package

Additional context
none