Fix Queries.BlobSize

[mrstanb]

This PR is an attempt to fix the issue described in #1119:

• make test seems to pass just fine locally -> hence, hopefully nothing is broken
• With the test program from Queries.BlobSize returns the contents of a blob instead of its size #1119 (cf. below), calling Queries.BlobSize for the pointer ptr in the line with the comment //BlobSize now seems to return the size 5, respectively [5, 5] when using intervals.

Test program from #1119:

#include <stdlib.h>

int main(int argc, char const *argv[]) {
    char *ptr = malloc(5 * sizeof(char));

    *ptr = 'a';

    free(ptr); //BlobSize

    return 0;
}

[mrstanb]

Is this good to merge?