main-coverity-AthenaMonitoringKernel

Coverity defect 19781: Line 56 (return vars.var[0]->size();) is unreachable. All cases, with returns, were handled in the previous 'if' structure so the last line of the 'fill' function was dead code. I made this explicit and adjusted the indentation to make the 'if' nesting clearer

Targeting 'main'; this is a code quality issue. Tagging author @llewitt in case this was not their intention.