…gin routes. (elastic#84605)

Passing in an empty string '' to useResolver() would trigger a wild card search across all indices and fields, potentially causing a timeout and the page would fail to load. The following pages were affected: Single Metric Viewer, Data frame analytics models list, Data frame analytics jobs list, Data frame analytics exploration page, File Data Visualizer (Data visualizer - Import data from a log file). This PR fixes it by passing undefined instead of '' to useResolver to avoid calling _fields_for_wildcard with an empty pattern. Jest tests were added to cover the two parameter scenarios empty string/undefined.