Fix access on undefined script object

I saw the following stacktrace while running Chromium locally:

[205430:205430:1007/182130.681774:ERROR:CONSOLE(61)] "TypeError: Cannot read property 'originStackTrace' of null TypeError: Cannot read property 'originStackTrace' of null
    at Function._script (devtools://devtools/bundled/sources/sources_module.js:1469:197)
    at Sources.ScriptOriginPlugin.rightToolbarItems (devtools://devtools/bundled/sources/sources_module.js:1467:41)
    at Sources.UISourceCodeFrame.syncToolbarItems (devtools://devtools/bundled/sources/sources_module.js:335:215)
    at Sources.SourcesView._updateScriptViewToolbarItems (devtools://devtools/bundled/sources/sources_module.js:1215:168)
    at Sources.SourcesView._editorClosed (devtools://devtools/bundled/sources/sources_module.js:1226:43)
    at Sources.TabbedEditorContainer.dispatchEventToListeners (devtools://devtools/bundled/common/Object.js:12:173)
    at Sources.TabbedEditorContainer._tabClosed (devtools://devtools/bundled/sources/sources_module.js:1012:114)
    at TabbedPane.dispatchEventToListeners (devtools://devtools/bundled/common/Object.js:12:173)
    at TabbedPane._innerCloseTab (devtools://devtools/bundled/ui/TabbedPane.js:30:73)
    at TabbedPane.closeTabs (devtools://devtools/bundled/ui/TabbedPane.js:23:93)", source: devtools://devtools/bundled/host/InspectorFrontendHost.js (61)

It appears that the code in this file already assumes that script can be
undefined, but forgot this particular case.

Change-Id: I7b0c0d34b4d16a1d29656cd8d86e3f290f8bb227
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1845751
Commit-Queue: Tim Van der Lippe <tvanderlippe@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Auto-Submit: Tim Van der Lippe <tvanderlippe@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703397}

third_party/blink/renderer/devtools/front_end/sources/ScriptOriginPlugin.js

@@ -51,7 +51,7 @@ Sources.ScriptOriginPlugin = class extends Sources.UISourceCodeFrame.Plugin {
     const locations = Bindings.debuggerWorkspaceBinding.uiLocationToRawLocations(uiSourceCode, 0, 0);
     for (const location of locations) {
       const script = location.script();
-      if (script.originStackTrace) {
+      if (script && script.originStackTrace) {
         return script;
       }
     }