Scripting: SoarNav: Fix LUA checker warnings (i hope)

Author: robustini

libraries/AP_Scripting/applets/SoarNav.lua

@@ -124,7 +124,7 @@ Script Parameters (SNAV_*)
 
 --[[ SCRIPT INITIALIZATION ]]--
 
-math.randomseed(tonumber(tostring(millis() or 0)))
+math.randomseed(tonumber(tostring(millis() or 0)) or 0)
 
 -- Enums for GCS message severity and script internal state
 local MAV_SEVERITY = {