[BUG] `a'a` fills in all blocks

[mtfishman]

For example:

using BlockArrays: Block
using BlockSparseArrays: BlockSparseMatrix

a = BlockSparseMatrix{Float64}(undef, [2, 3], [2, 3])
a[Block(1, 1)] = randn(2, 2)
a[Block(2, 2)] = randn(3, 3)

julia> a
2×2-blocked 5×5 BlockSparseMatrix{Float64, Matrix{Float64}, …, …}:
 -1.10318   0.582626  │    ⋅          ⋅          ⋅       
 -1.04284  -2.18239   │    ⋅          ⋅          ⋅       
 ─────────────────────┼──────────────────────────────────
   ⋅         ⋅        │  -0.349282  -0.208514  -0.628124 
   ⋅         ⋅        │  -2.15969    2.31498   -0.730257 
   ⋅         ⋅        │   0.390346   1.51636   -0.0331465

julia> a'a
2×2-blocked 5×5 BlockSparseMatrix{Float64, Matrix{Float64}, …, …}:
 2.30452  1.63314  │   0.0       0.0       0.0     
 1.63314  5.10226  │   0.0       0.0       0.0     
 ──────────────────┼───────────────────────────────
 0.0      0.0      │   4.93862  -4.3349    1.78358 
 0.0      0.0      │  -4.3349    7.70197  -1.60982 
 0.0      0.0      │   1.78358  -1.60982   0.928913

julia> a * a
2×2-blocked 5×5 BlockSparseMatrix{Float64, Matrix{Float64}, …, …}:
 0.609417  -1.91426  │    ⋅          ⋅         ⋅      
 3.42632    4.15522  │    ⋅          ⋅         ⋅      
 ────────────────────┼────────────────────────────────
  ⋅          ⋅       │   0.327139  -1.36234   0.392481
  ⋅          ⋅       │  -4.53035    4.70213  -0.309774
  ⋅          ⋅       │  -3.42415    3.37869  -1.35142 

[ogauthe]

Isn't this the same as #24?

[mtfishman]

Oh yeah, I forgot about that one.