Allocation dialog: Error messages are not shown in dialog

[morremeyer]

Describe the bug
When setting an allocation in the allocation dialog leads to an error, the error is not shown in the dialog, but instead in the main page.

To Reproduce
Steps to reproduce the behavior:

1. Edit any allocation in the dashboard
2. Set the "Set to amount" field to an empty value
3. Click save
4. Nothing happens
5. Click cancel
6. See that the dashboard now shows an error

Expected behavior
Errors produced in the allocation dialog should be shown in that dialog.
They should also be cleared when the dialog is closed