Fix setting source settings without default value

Example text source's text field didn't have default value.
So, if never set before, can't be set using the "Source" action type.

Needed now that it is possible to create new sources via macro.

plugins/base/utils/source-setting.hpp

@@ -20,6 +20,7 @@ public:
 	bool Save(obs_data_t *obj) const;
 	bool Load(obs_data_t *obj);
 	std::string GetID() const { return _id; }
+	obs_property_type GetType() const { return _type; }
 	bool IsList() const;
 	bool operator==(const SourceSetting &other) const;