[Bug] SegFault on gradvector test when run with multithreading

[joshichaitanya3]

Describe the bug The gradvector test fails when run with multi-threading.

To Reproduce

1. Go to test/functionals/areaintegral
2. Run morpho6 -w4 gradvector.morpho

Expected behavior Output:

0
[ 1 ]
[ 0 ]
[ 0 ]
[ 2 ]

Actual output:

0
zsh: segmentation fault  morpho6 -w4 gradvector.morpho

This issue also calls for a separate automated test with the run command being morpho6 -w2 or something. Will have to look into its feasibility.