((floor(mr/2)==ceil(mr/2)) | (floor(mc/2)==ceil(mc/2)))
((number of rows is even) OR (number of columns is even))
Which is a peculiar way to do the test, but it should work fine.
That said, there are two OR operators:
| is a general elementwise logical OR that can be used on arrays
|| is the logical OR with short-circuit functionality. This is potentially more efficient, but only works with scalar logical arguments
In this case, you could use either, but using || would be preferred.
If MLINT was putting a squiggle under the lone |, that was probably why. It's not an error. It's just a hint.