Fixed getOption and rename to isOption

Fixed getOption who always return nil.
Rename getOption to isOption.

modules/corelib/ui/uicombobox.lua

@@ -19,13 +19,14 @@ function UIComboBox:clearOptions()
   self:clearText()
 end
 
-function UIComboBox:getOption(text)
-  if not self.options then return nil end
+function UIComboBox:isOption(text)
+  if not self.options then return false end
   for i,v in ipairs(self.options) do
     if v.text == text then
-      return nil
+      return true
     end
   end
+  return false
 end
 
 function UIComboBox:setOption(text, dontSignal)