Zero and sanity check all dynamic allocs.

This addresses the memory issues in Issue #6 expressed in
calloc_some.pdf and malloc_some.pdf
static const char *get_type(FILE *fp, int obj_id, const xref_t *xref)
{
    int          is_stream;
    char        *c, *obj, *endobj;
    static char  buf[32];
    long         start;

    start = ftell(fp);

    if (!(obj = get_object(fp, obj_id, xref, NULL, &is_stream)) || 
        is_stream                                               ||
        !(endobj = strstr(obj, "endobj")))
    {
        free(obj);
        fseek(fp, start, SEEK_SET);

        if (is_stream)
          return "Stream";
        else
          return "Unknown";
    }

    /* Get the Type value (avoiding font names like Type1) */
    c = obj;
    while ((c = strstr(c, "/Type")) && (c < endobj))
      if (isdigit(*(c + strlen("/Type"))))
      {
          ++c;
          continue;
      }
      else
        break;

    if (!c || (c && (c > endobj)))
    {
        free(obj);
        fseek(fp, start, SEEK_SET);
        return "Unknown";
    }

    /* Skip to first blank/whitespace */
    c += strlen("/Type");
    while (isspace(*c) || *c == '/')
      ++c;

    /* Return the value by storing it in static mem */
    memcpy(buf, c, (((c - obj) < sizeof(buf)) ? c - obj : sizeof(buf)));
    c = buf;
    while (!(isspace(*c) || *c=='/' || *c=='>'))
      ++c;
    *c = '\0';

    free(obj);
    fseek(fp, start, SEEK_SET);

    return buf;
}

static const char *get_type(FILE *fp, int obj_id, const xref_t *xref)
{
    int          is_stream;
    char        *c, *obj, *endobj;
    static char  buf[32];
    long         start;

    start = ftell(fp);

    if (!(obj = get_object(fp, obj_id, xref, NULL, &is_stream)) || 
        is_stream                                               ||
        !(endobj = strstr(obj, "endobj")))
    {
        free(obj);
        fseek(fp, start, SEEK_SET);

        if (is_stream)
          return "Stream";
        else
          return "Unknown";
    }

    /* Get the Type value (avoiding font names like Type1) */
    c = obj;
    while ((c = strstr(c, "/Type")) && (c < endobj))
      if (isdigit(*(c + strlen("/Type"))))
      {
          ++c;
          continue;
      }
      else
        break;

    if (!c || (c && (c > endobj)))
    {
        free(obj);
        fseek(fp, start, SEEK_SET);
        return "Unknown";
    }

    /* Skip to first blank/whitespace */
    c += strlen("/Type");
    while (isspace(*c) || *c == '/')
      ++c;

    /* Return the value by storing it in static mem */
    memcpy(buf, c, (((c - obj) < sizeof(buf)) ? c - obj : sizeof(buf)));
    c = buf;
    while (!(isspace(*c) || *c=='/' || *c=='>'))
      ++c;
    *c = '\0';

    free(obj);
    fseek(fp, start, SEEK_SET);

    return buf;
}
