ffprobe: Fix null pointer dereference with color primaries

Found-by: AD-lab of venustech
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
static const char *csv_escape_str(AVBPrint *dst, const char *src, const char sep, void *log_ctx)
{
    char meta_chars[] = { sep, '"', '\n', '\r', '\0' };
    int needs_quoting = !!src[strcspn(src, meta_chars)];

    if (needs_quoting)
        av_bprint_chars(dst, '"', 1);

    for (; *src; src++) {
        if (*src == '"')
            av_bprint_chars(dst, '"', 1);
        av_bprint_chars(dst, *src, 1);
    }
    if (needs_quoting)
        av_bprint_chars(dst, '"', 1);
    return dst->str;
}

static const char *csv_escape_str(AVBPrint *dst, const char *src, const char sep, void *log_ctx)
{
    char meta_chars[] = { sep, '"', '\n', '\r', '\0' };
    int needs_quoting = !!src[strcspn(src, meta_chars)];

    if (needs_quoting)
        av_bprint_chars(dst, '"', 1);

    for (; *src; src++) {
        if (*src == '"')
            av_bprint_chars(dst, '"', 1);
        av_bprint_chars(dst, *src, 1);
    }
    if (needs_quoting)
        av_bprint_chars(dst, '"', 1);
    return dst->str;
}
