Bug with the `fastVDiag()` function

[haziqj]

Somehow, re-running the function on the same arguments returns different answers each time. Suspect that it keeps some results in memory and re-uses it.

> H <- fnH3(rnorm(5))
> fastVDiag(H, 1:5)
            [,1]       [,2]        [,3]       [,4]       [,5]
[1,]  0.26970789 -0.1506874 -0.08902361 -0.3817465  0.3517496
[2,] -0.15068739  4.6687736 -2.03456593 -3.1172434  0.6337231
[3,] -0.08902361 -2.0345659  1.09680087  1.5941589 -0.5673703
[4,] -0.38174646 -3.1172434  1.59415895  3.0434338 -1.1386029
[5,]  0.35174956  0.6337231 -0.56737028 -1.1386029  0.7205005
> fastVDiag(H, 1:5)
          [,1]       [,2]       [,3]       [,4]       [,5]
[1,]  3.345030   3.128946  -3.800166  -9.258419   6.584607
[2,]  3.128946  36.077689 -16.682934 -32.035877   9.512176
[3,] -3.800166 -16.682934  11.084884  19.345309  -9.947093
[4,] -9.258419 -32.035877  19.345309  42.646019 -20.697033
[5,]  6.584607   9.512176  -9.947093 -20.697033  14.547343
> fastVDiag(H, 1:5)
           [,1]       [,2]      [,3]      [,4]      [,5]
[1,]   65.34335   67.02975  -84.8986 -189.4826  142.0081
[2,]   67.02975  404.40627 -184.4152 -424.4495  137.4287
[3,]  -84.89860 -184.41523  155.6321  307.8244 -194.1427
[4,] -189.48262 -424.44951  307.8244  711.1323 -405.0246
[5,]  142.00813  137.42871 -194.1427 -405.0246  319.7304