Fix detection of Fluid Mode

[lucash]

In Javascript the || operator does not necessarily return true or false,
but it returns the first value (if it is truthy) or the second value (if
the first value is falsey). This made this method return numbers instead
of booleans while the return value is compared to booleans with the
strict equal (===) operator which then gave wrong results.

[coveralls]

Coverage remained the same at 73.832% when pulling 2701947 on lucash:fix-fluid-mode-detection into 5ddf254 on mediaelement:master.

[lucash]

The && operator works similar: It will return the first value if that is falsey, otherwise it will return the second value. Also see MDN: Logical Operators.

[rafa8626]

Thanks for the info. I'll check the places where ~ is being used and make sure I use !== -1 instead to avoid this issue.

[rafa8626]

PR merged. Thanks