IMU uses wrong error value for checking errors

[drdeaton]

Describe the bug
When using the okapi::IMU, sometimes pros::c::imu_get_euler gives an error value, setting errno. This results in the euler containing PROS_ERR_F values, but okapi::IMU::get() instead checks for PROS_ERR values, leading to the error not being handled properly.

Steps To Reproduce
Reset an IMU and try to use it before it finishes resetting.

Expected behavior
IMU::get() should return PROS_ERR_F

Versions
The bug was discovered while running OkapiLib 4.8.0 and PROS kernel 3.7.3