fix: the appearance of indents when height = 1.0 or width = 1.0

[astrelinvl]

fix #366

[dmtrKovalenko]

The problem with your change is that they apply to all sizes, not just fullscreen. Consider
width = 0.8, height = 0.8 (the defaults):
- center_col would be calculated as math.floor((200 - 160) / 2) - 1 = 19 instead of 20 — the picker shifts one cell left
- center_row shifts one cell upward similarly
- total_height gets an extra row that wasn't taken into account in the height calculation

[dmtrKovalenko]

can you please check on the main if you still have this issue?

[astrelinvl]

When
prompt_position = 'top',
preview_position = 'right',

or

prompt_position = 'top',
preview_position = 'bottom',

or

prompt_position = 'bottom',
preview_position = 'bottom',

statusline is visible + borders are drawn incorrectly