Completion list seems not to scroll

[theldoria]

The completion list seems not to scroll if it is larger than the visual buffer.

Indeed it start scrolling if one sellects elements down in the list, triggering the lists scoll, but before one reaches that point nothing visually happens.

Reason is, that the completion list is clipped at the buffer boundary. The list should checl how many space the buffer has instead of using a constant visual size...