vigranumpy: added precondition for zero strides
vigranumpy: added precondition for zero strides

dagophil/vigra,funkey/vigra,dstoe/vigra,dagophil/vigra,dagophil/vigra,dagophil/vigra,dstoe/vigra,dstoe/vigra,dstoe/vigra,dstoe/vigra,funkey/vigra,funkey/vigra,funkey/vigra,dagophil/vigra,dagophil/vigra,dstoe/vigra,funkey/vigra,funkey/vigra,funkey/vigra,dstoe/vigra,dagophil/vigra