[9.0][FIX] Correct check of property 'rules'

[MouTio]

Description of the issue/feature this PR addresses:
#22517

Current behavior before PR:
In some browsers, like Chrome 64, there is an exception when the property 'rules' is not located in CSS sheets and the user tries to enter to some sections, like 'Preferences'.

Desired behavior after PR is merged:
'rules' property is correctly checked and the execution continues in every browsers.

--
I confirm I have signed the CLA and read the PR guidelines at www.odoo.com/submit-pr

[leemannd]

Thanks for the fix

[ged-odoo]

I couldn't accept this PR because the CLA check did not pass. However, I just pushed a fix in 9.0. Thank you for your contribution

[MouTio]

@ged-odoo I don't know why the CLA check did not pass.

I have signed the CLA and read the PR guidelines at www.odoo.com/submit-pr

And it is commited in 8c941cb (Jan 31, 2018 of branch 9.0)

[traviswaelbro]

@ged-odoo @MouTio I've had a similar issue with CLA failing for no apparent reason, so I would be interested to know why as well.

[ged-odoo]

that is curious indeed. Sorry for that, I'll have a better look next time the issue arises

[aryeharmon]

hasOwnProperty('rules') always returns false

[MouTio]

@aryeharmon yes. That is because there is no property 'rules'. Anyway, the BUG here was the check of that property. The existance or not of the property is another matter.