Fix double increment.
Fix double increment.

Inside double-conversion this function is only called with values that will
never trigger this bug.

floitschG/double-conversion,bugdebugger/double-conversion,smspillaz/double-conversion,bugdebugger/double-conversion,floitschG/double-conversion,vitaut/double-conversion,floitsch/double-conversion,bos/double-conversion,smspillaz/double-conversion,floitsch/double-conversion,google/double-conversion,project-zerus/double-conversion,google/double-conversion,google/double-conversion,project-zerus/double-conversion,bos/double-conversion,bos/double-conversion,vitaut/double-conversion