🐛[BUG] - `Imu::is_calibrating` returns `true` if imu is not connected

[SizzinSeal]

Describe the bug Imu::is_calibrating returns true if imu is not connected

To Reproduce Steps to reproduce the behavior:

1. Instantiate an IMU on a port where it is not connected
2. call Imu::is_calibrating()

Expected behavior It should return false

Screenshots If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• PROS 3.8.0

[WillXuCodes]

Closed by #628

[WillXuCodes]

Not closing this yet due to #628 not being merged yet.

[SizzinSeal]

Reproduced in kernel version 3.8.3