Remove null terminations in fwver string when reading from Steelseries Apex keyboards.

!951 (merged) broke profile loading for Steelseries Apex users. This was caused by a version string mismatch between the profile on disk and what is in the RGBController at runtime. In the latter case, the firmware version string was stored raw with null characters whereas these are stripped when the profile is written to disk and displayed on the GUI.

Remove null characters from fwver string before returning it to the RGBController.