Display corruption after using file completion when numbering is enabled

[johnsonjh]

Display corruption after completion when numbering.

To reproduce:

1. Open a file that uses all visible screen lines.
   
2. :set filec=^ num
   
3. :e ^
   
4. [space]
   

This seems to affect all versions of nvi from at least 1.79.

Confirmed in 5fcdc13

[lichray]

Confirmed.

[johnsonjh]

PR #107 is related and a workaround - but not yet a fix. Maybe you'll track it down before me. :)