Update SGSparseMatrix.cpp
Update SGSparseMatrix.cpp

Fixes segmentation fault when num_features > num_vectors.
Saurabh7/shogun,shogun-toolbox/shogun,karlnapf/shogun,Saurabh7/shogun,Saurabh7/shogun,karlnapf/shogun,sorig/shogun,sorig/shogun,Saurabh7/shogun,sorig/shogun,shogun-toolbox/shogun,shogun-toolbox/shogun,shogun-toolbox/shogun,besser82/shogun,Saurabh7/shogun,Saurabh7/shogun,shogun-toolbox/shogun,sorig/shogun,shogun-toolbox/shogun,Saurabh7/shogun,lisitsyn/shogun,lambday/shogun,lisitsyn/shogun,besser82/shogun,lisitsyn/shogun,lisitsyn/shogun,besser82/shogun,geektoni/shogun,karlnapf/shogun,lisitsyn/shogun,sorig/shogun,geektoni/shogun,karlnapf/shogun,geektoni/shogun,lambday/shogun,lambday/shogun,Saurabh7/shogun,lambday/shogun,karlnapf/shogun,karlnapf/shogun,besser82/shogun,besser82/shogun,geektoni/shogun,lambday/shogun,Saurabh7/shogun,lisitsyn/shogun,geektoni/shogun,sorig/shogun,geektoni/shogun,besser82/shogun,lambday/shogun