Avoid overflow with simplehash

Hi,

SimpleHash.

The function SH_START_ITERATE can trigger some overflow.

See:

typedef struct SH_ITERATOR
{
uint32 cur; /* current element */
uint32 end;
bool done; /* iterator exhausted? */
} SH_ITERATOR;

The cur field is uint32 size and currently can be stored a uint64,

which obviously does not fit.

Also, the current index is int, which is possibly insufficient 

since items can be up to uint32.

Attached a fix.

best regards,

Ranier Vilela