3D volume preview still does not work, with error "External data not ready for index 0"

[fangq]

@harikiranrommala, I tested the current staging branch after closing #12, I noticed that many of them can not be rendered

for example, most of the openneuro externally linked data can not be previewed

https://zodiac.coe.neu.edu/dev/staging/databases/openneuro/ds000001

main.js:1 react-json-view error: src property must be a valid json object
Fe.validateState @ main.js:1
preview.js:237 ❌ External data not ready for index 0
cJ @ preview.js:237
preview.js:237 ❌ External data not ready for index 0
cJ @ preview.js:237
preview.js:237 ❌ External data not ready for index 0
cJ @ preview.js:237
/dev/io_fav.png:1 
            
            
           Failed to load resource: the server responded with a status of 404 (Not Found)
main.js:1 react-json-view error: src property must be a valid json object
Fe.validateState @ main.js:1
preview.js:237 ❌ External data not ready for index 0
cJ @ preview.js:237
main.js:1 react-json-view error: src property must be a valid json object
Fe.validateState @ main.js:1