mul! with Symmetric does not check sizes are compatible

[sethaxen]

Here we define matrices A, B, and C with incompatible sizes for multiplication:

julia> using LinearAlgebra

julia> A = Symmetric(randn(5, 5));

julia> B = randn(10, 5);

julia> C = zeros(5, 5);

julia> mul!(C, A, B)
5×5 Array{Float64,2}:
  0.98847    1.64837    0.00974132  -4.00331    0.138057
 -2.00759   -1.08226   -0.240299     1.32073   -0.144493
  0.535827   0.125398  -0.53018     -0.385373  -0.146108
 -3.96372   -2.00857   -1.01928      4.40731    1.87013 
 -2.91995   -1.37546   -1.09736      4.79497    1.76239 
 
julia> A * B
5×5 Array{Float64,2}:
  0.98847    1.64837    0.00974132  -4.00331    0.138057
 -2.00759   -1.08226   -0.240299     1.32073   -0.144493
  0.535827   0.125398  -0.53018     -0.385373  -0.146108
 -3.96372   -2.00857   -1.01928      4.40731    1.87013 
 -2.91995   -1.37546   -1.09736      4.79497    1.76239 

Yet mul! (and *) works! I have confirmed that this has been the behavior since Julia 1.0.