Random missing thumbnails & constrained ability to zoom when images are present

[caaster]

[mejackreed]

A few quick fixes from the Leaflet side:

• set tileSize: 512 on instantiation of the L.TileLayer.Iiif object
  OR
• This update of Leaflet-IIIF aims to solve this problem Better tile size support mejackreed/Leaflet-IIIF#68

[ggeisler]

Some examples that might be helpful in either further investigating the problem or testing to see if the recommendations from @mejackreed above will solve the problem:

Use the published Matter exhibit and edit the browse category Commercial Work. When using these objects as the thumbnail source (in the From this exhibit autocomplete field), they load in the crop window zoomed in and the zoom out control is disabled:

• Atomic head; Arts & Architecture cover December, 1946.
• Jackson Pollock painting.

On the other hand, these images load normally (zoomed out):

• Film strips; Photogram; Fortune magazine cover July, 1948.
• Shirley Temple doll head molds.