lua fixes

modules/core_lib/settings.lua

@@ -27,12 +27,7 @@ function Settings.remove(key)
 end
 
 function Settings.set(key, value)
-  local valuestr = convertSettingValue(value)
-  if valuestr == '' then
-    g_configs.remove(key)
-  else
-    g_configs.set(key, convertSettingValue(value))
-  end
+  g_configs.set(key, convertSettingValue(value))
 end
 
 function Settings.setDefault(key, value)

modules/core_lib/util.lua

@@ -76,3 +76,10 @@ function toboolean(str)
   end
   return false
 end
+
+local oldtonumber = tonumber
+function tonumber(v)
+  local v = oldtonumber(v)
+  if not v then return 0 end
+  return v
+end