Fix MatMul assumptions tests
Fix MatMul assumptions tests

An empty MatMul now gives 1 instead of a MatMul object. Handle this in the
handlers code.

yashsharan/sympy,Titan-C/sympy,aktech/sympy,jerli/sympy,madan96/sympy,kaushik94/sympy,lindsayad/sympy,mafiya69/sympy,skidzo/sympy,oliverlee/sympy,Arafatk/sympy,jerli/sympy,drufat/sympy,jaimahajan1997/sympy,aktech/sympy,postvakje/sympy,sampadsaha5/sympy,Titan-C/sympy,hargup/sympy,souravsingh/sympy,oliverlee/sympy,souravsingh/sympy,Arafatk/sympy,Arafatk/sympy,rahuldan/sympy,hargup/sympy,madan96/sympy,oliverlee/sympy,Shaswat27/sympy,lindsayad/sympy,Shaswat27/sympy,madan96/sympy,drufat/sympy,jerli/sympy,lindsayad/sympy,postvakje/sympy,Curious72/sympy,ChristinaZografou/sympy,rahuldan/sympy,skidzo/sympy,yashsharan/sympy,kaichogami/sympy,kaichogami/sympy,chaffra/sympy,Curious72/sympy,mafiya69/sympy,yashsharan/sympy,ChristinaZografou/sympy,mafiya69/sympy,kaushik94/sympy,jaimahajan1997/sympy,jaimahajan1997/sympy,drufat/sympy,ChristinaZografou/sympy,Titan-C/sympy,Curious72/sympy,souravsingh/sympy,chaffra/sympy,rahuldan/sympy,Shaswat27/sympy,chaffra/sympy,kaushik94/sympy,postvakje/sympy,hargup/sympy,skidzo/sympy,aktech/sympy,sampadsaha5/sympy,kaichogami/sympy,sampadsaha5/sympy