Simplify control flow in xmlParseStartTag2

Remove some goto labels and deduplicate a bit of code after handling
namespaces.

Before:

    loop {
        parseAttribute
        if (ok) {
            if (defaultNamespace) {
                handleDefaultNamespace
                if (error)
                    goto skip_default_ns;
                handleDefaultNamespace
    skip_default_ns:
                freeAttr
                nextAttr
                continue;
            }
            if (namespace) {
                handleNamespace
                if (error)
                    goto skip_ns;
                handleNamespace
    skip_ns:
                freeAttr
                nextAttr;
                continue;
            }
            handleAttr
        } else {
            freeAttr
        }
        nextAttr
    }

After:

    loop {
        parseAttribute
        if (!ok)
            goto next_attr;
        if (defaultNamespace) {
            handleDefaultNamespace
            if (error)
                goto next_attr;
            handleDefaultNamespace
        } else if (namespace) {
            handleNamespace
            if (error)
                goto next_attr;
            handleNamespace
        } else {
            handleAttr
        }
    next_attr:
        freeAttr
        nextAttr
    }