BUG: initialize InverseCovariance size with degenerate matrix

This patch fixes a segfault with VectorConfidenceConnected when used
with VectorImages and only one initial seed. This was caused by an
inverse matrix not being initialized correctly for variable length
measurement vectors.

Change-Id: I81bd2c9afe35f726d552c08849dd3c80710bca05
Merge topic 'VectorConfidenceConnectedInvCovarSegfault'

b07b051 BUG: initialize InverseCovariance size with degenerate matrix