templater: fix list templating bug High-level use case: printing a list of objects with formatter when each object in turn contains a list of properties (like when % template symbol is used in {things % '{thing}'} Let the top-level list contain one thing with two properties: objs = [{ 'props': [ { 'value': 1, 'show': 1 }, { 'value': 2 }] }] (please note that second property does not have 'show' key) If a templateformatter is used to print this with template "{props % '{if(show, value)}'}" current implementation will print value for both properties, which is a bug. This happens because in `templater.runmap` function we only rewrite mapping values with existing new values for each item. If some mapping value is missing in the item, it will not be removed.