Crash happened when adjusting operator props in Adjust Last Operation
panel.

When there are more than 32 objects selected in muti-object-editmode, we
are running into RNA array limit (objects_selection_count is defined as
an RNA array (which can only hold 32 entries, see
RNA_MAX_ARRAY_LENGTH), leading to reading random memory errors.

While there might be ways to make this work with more than 32 selected
objects, this patch only cancels the operator with a report message
(instead of crashing).