import assistant: fix variable width after guesser with output constraints

import assistant: fix variable width after guesser with output constraints

The current code fixes the guessed variable width according to
input constraints. But the data output stages checks the
width against output constraints. The minimum width for FMT_E
is 1 for input and 6 for output. When the guesser proposes FMT_E
with width 5, then 5 is chosen. With this patch, the width is
fixed to 6.

Thanks to Fatemeh Ilkhani for reporting the bug and providing a
csv that triggers the crash.

Closes: https://savannah.gnu.org/bugs/?66456