[PropertyView] MultiValues of type 'text' disappear on save

[mpsonntag]

On some occasions, when a Property contains multiple values of type text that also contain multiple lines and the document is saved to a file and loaded again, the multi values except for the very first will be lost. The first value will also be truncated and only contain the first line of the original value.

[fschrader1992]

The problem seems to occur when setting the value, as after adding two values to the same property and closing the text editor, this error occurs:

Gtk-CRITICAL **: gtk_tree_view_unref_tree_helper: assertion 'node != NULL' failed

Adding several properties with only one value containing long text saves and reloads normally.