squeeze_matrix fails when no mask provided

[NPounder]

Providing only a matrix doesn't work and produces strange results. Fails unit test test_squeeze_just_matrix.
(Initial unit tests can be found in the tests branch on my fork)

[jgomezdans]

Should be easy to fix, it's around https://github.com/jgomezdans/KaFKA/blob/master/kafka/utils.py#L66