Guard frontend AOIs without land cover
Guard frontend AOIs without land cover

- show an error alert message and prevent running MapShed when the
  analysis results data indicates that the AOI doesn't include any land
  cover

kdeloach/model-my-watershed,project-icp/bee-pollinator-app,WikiWatershed/model-my-watershed,WikiWatershed/model-my-watershed,WikiWatershed/model-my-watershed,kdeloach/model-my-watershed,kdeloach/model-my-watershed,project-icp/bee-pollinator-app,kdeloach/model-my-watershed,project-icp/bee-pollinator-app,kdeloach/model-my-watershed,WikiWatershed/model-my-watershed,project-icp/bee-pollinator-app,WikiWatershed/model-my-watershed