[eigen] SparseQR crashes on rectangular matrix

[Pavel Holoborodko <pavel@xxxxxxxxxxxxxxx>]

SparseQR crashes in coletree when applied for rectangular matrix with rows < cols.

After quick study - apparently coletree doesn't support rectangular matrices.

Vector firstRowElt is allocated with rows() size (line #73).  

However it is indexed as having cols() size in the code (lines #75, #108).

Would appreciate any help in this regard.

Thank you in advance.

Pavel.