Bugfix: is_refinable usage

[sandro-elsweijer]

Closes #1599

Describe your changes here:
The element_is_refinable usage was wrong.

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[holke]

Looks good.

But the adapt call in the recursive adaptation must also be changed.

t8code/src/t8_forest/t8_forest_adapt.cxx

Line 346 in 8a1ac0b

if (refine == 1) {

[sandro-elsweijer]

Looks good.

But the adapt call in the recursive adaptation must also be changed.

t8code/src/t8_forest/t8_forest_adapt.cxx

Line 346 in 8a1ac0b

if (refine == 1) {

Nice catch! Done