science/isaac-cfd: Unbreak build with GCC 10

march.F:1111:47:

1111 | 1 Q, PROPS, NPPTS, S, VOL, DTJ,

|                                               1

Error: Rank mismatch in argument 'vol' at (1) (scalar and rank-3)

http://package18.nyi.freebsd.org/data/121amd64-default-PR244494/2020-06-10_18h04m44s/logs/errors/isaac-4.2_16.log

PR: 246700