majority_vote confuses Ising and QUBO problems

**Description**
In file 'chain_breaks.py', line 213 is

if samples.all(): # spin-valued

checking whether the samples consist only of +1 and -1, in which case the submitted problem is determined to be an Ising. But that doesn't work for some outputs since, in addition to -1 and +1, there may be 0 values corresponding to (I guess) unused qubits. Those zeros confuse the test on l. 213 and it incorrectly determines the problem to be a QUBO (since samples.all() is false).

I fixed that, in my case, by replacing line 213 with

if np.amin(samples) == -1: # spin-valued

In some rare cases all valid spins of an Ising problem solution might be +1, in which case the proposed test would also fail. But then, I guess, the output of majority_vote, as implemented, should be the same regardless of whether it is an Ising or a QUBO problem.