Diff Error: Empty new lines above bullet point breaks amendment

[MSoeb]

Describe the bug
New empty lines above a bullet point in an amendment leads to an error. The amendment can't be loaded and the main motion can't show the amendments.

How to Reproduce
Steps to reproduce the behavior:

1. open a meeting
2. open motions
3. create a motion with a bullet point
4. create an amendment on the bullet point. add two empty lines above the bullet point. --> amendment is broken and amendments in motion can't be loaded. also amendment list can't be loaded.

Expected behavior
By adding empty lines above a bullet point, the amendment should not broken by saving it. This should be done by erasing the empty lines by saving. The amendment should than display an information, that no change is done.

Additional context
Part of META Issue #2956. An example cant' be provided, because this would break amendment list views.

[bastianjoel]

Already fixed see #4508