Set large odometry variance when odometry is reset by Odom/ResetCountdown

[matlabbe]

When odometry is automatically reset to last pose when lost, RTAB-Map cannot know there is a discontinuity (it only detects if odometry is reset to Identity, creating a new map). When resetting to previous pose, make sure that on the next odometry update, odometry is sent with large variance.

[matlabbe]

After verification for the standalone, the variance is set to 1 when the first frame is computed (as the first variance returned is always 0). See here.

For ROS, null variance is sent (see here). If info.variance is 0, 1 should be set instead.

[matlabbe]

should be fixed by c1c62b0