MD_ReconstructionFromNode returns pointers to local variables

[mmozeiko]

MD_ReconstructionFromNode in out list returns pointers to local variables:
https://github.com/Dion-Systems/metadesk/blob/23289461d249c787ff631ba1f82535b20acefe68/source/md.c#L4137 and
https://github.com/Dion-Systems/metadesk/blob/23289461d249c787ff631ba1f82535b20acefe68/source/md.c#L4170

This means that anybody using list outside will potentially read garbage values. This happens in sanity_tests.c tests when it tries to join strings immediately afterwards (but in current code it will return correct strings because stack values are not yet overwritten):

https://github.com/Dion-Systems/metadesk/blob/23289461d249c787ff631ba1f82535b20acefe68/tests/sanity_tests.c#L846

If you want to trigger this error, then inserting following piece of code after line 845 (directly below call to MD_ReconstructionFromNode) will produce corrupted string and test will fail:

            {
                // overwrite 4KB of stack with 0xaa 
                char* stack = (char*)_alloca(4096);
                for (volatile int k = 0; k < 4096; k++) stack[k] = 0xaa;
            }

I have potential fix for this here: mmozeiko@a18850f
It changes char variables to string literals. If you're ok with such change.