Make sure the details region exists.
Make sure the details region exists.

Ensure that the details region exists before attempting to put the
`DetailsView` into it.  If the user quickly leaves the analysis page
before the details region exists, then the region may no longer exist.

Connects to azavea/model-my-watershed#146

project-icp/bee-pollinator-app,kdeloach/model-my-watershed,kdeloach/model-my-watershed,mmcfarland/model-my-watershed,lliss/model-my-watershed,lliss/model-my-watershed,mmcfarland/model-my-watershed,mmcfarland/model-my-watershed,kdeloach/model-my-watershed,lewfish/model-my-watershed,project-icp/bee-pollinator-app,WikiWatershed/model-my-watershed,mmcfarland/model-my-watershed-1,lliss/model-my-watershed,lewfish/model-my-watershed,project-icp/bee-pollinator-app,lliss/model-my-watershed,mmcfarland/model-my-watershed,lewfish/model-my-watershed,mmcfarland/model-my-watershed-1,lewfish/model-my-watershed,WikiWatershed/model-my-watershed,lliss/model-my-watershed,kdeloach/model-my-watershed,mmcfarland/model-my-watershed-1,WikiWatershed/model-my-watershed,mmcfarland/model-my-watershed,project-icp/bee-pollinator-app,kdeloach/model-my-watershed,WikiWatershed/model-my-watershed,lewfish/model-my-watershed,WikiWatershed/model-my-watershed,mmcfarland/model-my-watershed-1