Fix Shelley inline diff view page crash in Firefox due to duplicate model creati

[josharian]

Discord Message

Author: c.o.s.m.o.
Channel: #feedback
Link: https://discord.com/channels/1405685085923049482/1405686161791516873/1459865756790558824

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new Shelley inline diff view causes the page to break in Firefox; it goes completely blank and then I get this error:

Error: ModelService: Cannot add model because it already exists!
    _createModelData modelService.js:288
    createModel modelService.js:297
    xpe standaloneCodeEditor.js:322
    qK standaloneCodeEditor.js:316
    vAe standaloneEditor.js:183
    Jv PatchTool.tsx:179
    React 3
    Bl scheduler.production.min.js:13
    Fl scheduler.production.min.js:14
    xu scheduler.production.min.js:14
    en main.js:1
    Su index.js:4
    en main.js:1
    Mf React
    en main.js:1
    Df React
    en main.js:1
    zf React
    en main.js:1
    <anonymous> main.tsx:2
react-dom.production.min.js:188:120
Uncaught Error: ModelService: Cannot add model because it already exists!
    _createModelData modelService.js:288
    createModel modelService.js:297
    xpe standaloneCodeEditor.js:322
    qK standaloneCodeEditor.js:316
    vAe standaloneEditor.js:183
    Jv PatchTool.tsx:179
    React 3
    Bl scheduler.production.min.js:13
    Fl scheduler.production.min.js:14
    xu scheduler.production.min.js:14
    en main.js:1
    Su index.js:4
    en main.js:1
    Mf React
    en main.js:1
    Df React
    en main.js:1
    zf React
    en main.js:1
    <anonymous> main.tsx:2
modelService.js:288:19