datastorage: fix use-after-free compiler error

[mmtj]

I am not familiar with how are dawn_regmem() and dawn_unregmem() supposed to be used, so I might be wrong.

Nevertheless, it seems odd to use FILE * fp pointer after fclose(), regardless how it is supposed to be handled in dawn_unregmem().

This should fix the "use-after-free" compiler error.

Closes: #198

[Flole998]

This is actually intended, the (un)reg_mem() functions keep track of memory usage, it is intended to be used as a memory leak detector and should be called after the memory is freed.

[PolynomialDivision]

Yes. Have a look here:
58861a1