Random store failures without any error reported

[Yuras]

See symisc/vedis#3. The same code is used in unqlite, and the same bugs exist.

There are 3 fixes to be applied: symisc/vedis#5, symisc/vedis#6, symisc/vedis#7

Here is example program to reproduce the issue (it is the vedis version adopted for unqlite)

#include <unqlite.h>

#include <stdlib.h>
#include <stdio.h>
#include <time.h>

// generate random bytes of variable (important!) length
char *randomBytes(int* len)
{
    *len = rand() % 4 + 1;
    char *res = (char*)malloc(*len);

    int i;
    for (i = 0; i < *len; i++)
    {
        res[i] = rand() % 256;
    }

    return res;
}

int main()
{
    unqlite *db;
    int res = unqlite_open(&db, "test.db", UNQLITE_OPEN_CREATE);
    if (res != UNQLITE_OK)
    {
        printf("Error opening unqlite: %i\n", (int)res);
        return 0;
    }

    srand(time(NULL));

    char buffer[255];
    unqlite_int64 inout;

    int block = 0;
    int count = 0;

    while(1)
    {
        int keyLen;
        int valLen;
        char *key = randomBytes(&keyLen);
        char *val = randomBytes(&valLen);

        // insert random key
        res = unqlite_kv_store(db, key, keyLen, val, valLen);
        if (res != UNQLITE_OK)
        {
            printf("Unable to store: %i\n", (int)res);
            return 0;
        }

        // verify it was stored correctly
        inout = 255;
        res = unqlite_kv_fetch(db, key, keyLen, &buffer[0], &inout);
        if (res != UNQLITE_OK)
        {
            printf("Unable to fetch: %i", (int)res);
            return 0;
        }

        // generate new random key and delete if it exists
        free(key);
        key = randomBytes(&keyLen);

        inout = 255;
        res = unqlite_kv_fetch(db, key, keyLen, &buffer[0], &inout);
        if (res == UNQLITE_OK)
        {
            res = unqlite_kv_delete(db, key, keyLen);
            if (res != UNQLITE_OK)
            {
                printf("Unable to delete: %i\n", (int)res);
                return 0;
            }
        }

        free(key);
        free(val);

        count++;
        if (count > 10000)
        {
            block++;
            count = 0;
            printf("%i 10K iterations\n", block);
        }
    }
    return 0;
}