Don't crash when parsing DRM MIME types

             mime, confidence);

    }

    if (!strncmp(mime, "drm", 3)) {

        const char *originalMime = strrchr(mime, '+') + 1;

        if (!strncmp(mime, "drm+es_based", 12)) {

    // DRM MIME type syntax is "drm+type+original" where

    // type is "es_based" or "container_based" and

    // original is the content's cleartext MIME type

    if (!strncmp(mime, "drm+", 4)) {

        const char *originalMime = strchr(mime+4, '+');

        if (originalMime == NULL) {

            // second + not found

            return NULL;

        }

        ++originalMime;

        if (!strncmp(mime, "drm+es_based+", 13)) {

            return new DRMExtractor(source, originalMime);

        } else if (!strncmp(mime, "drm+container_based", 19)) {

        } else if (!strncmp(mime, "drm+container_based+", 20)) {

            mime = originalMime;

        } else {

            return NULL;