Fix a typo and make delay non-negative in serial comms throttling code.
Fix a typo and make delay non-negative in serial comms throttling code.

codewithpassion/openrov-software,BrianAdams/openrov-software,codewithpassion/openrov-software,codewithpassion/openrov-software,BrianAdams/openrov-software,BrianAdams/openrov-software,BrianAdams/openrov-software,codewithpassion/openrov-software