BUG: Fix a bug in MCC function

Improve the fix added in e15f169.

In case of a flat region, GLCM has shape [1, 1, a], thereby resulting only in 1 eigenvalue (1). To prevent an indexing error, return arbitrary 1 in this case.

In certain cases linalg.eigvals returns a complex number. Cast to float to ensure just the real part is returned.

radiomics/glcm.py

@@ -642,7 +642,7 @@ def getMCCFeatureValue(self):
 
     MCC = numpy.sqrt(Q_eigenValue[:, -2])
 
-    return float(numpy.mean(MCC))  # 2nd highest eigenvalue
+    return numpy.mean(MCC).real  # 2nd highest eigenvalue
 
   def getIdmnFeatureValue(self):
     r"""