awk: fix use-after-free in "$BIGNUM1 $BIGGERNUM2" concat op

Second reference to a field reallocs/moves Fields[] array, but first ref
still tries to use the element where it was before move.

function                                             old     new   delta
fsrealloc                                             94     106     +12

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
1 file changed