Data loss without warning when editing a file with > 2^16 rows

[OmerShapira]

Repro steps:

• Create a csv with more than 2^16 rows (tested with 40 million)
• open in sc-im for edits
• save
• file now contains only first 2^16 rows.

Expected behavior:

• Under this current limitation of 2^16 rows, both opening should warn about only displaying first lines, and upon saving, a warning should be prompting to warn against data loss.
• Ideally no 2^16 row limitation should exist :)