Update bootstrap-node.js to check for Array.isArray

[MarkZuber]

Issue: #165288

As mentioned in the issue, we're seeing

[85180:1102/151514.317775:INFO:CONSOLE(231)] "%c  ERR color: #f33 [Extension Host] TypeError: Cannot read properties of null (reading 'length')
	at Module._resolveLookupPaths (/Users/zube/vscode-distro/out/bootstrap-node.js:83:38)
	at Module._resolveLookupPaths (/Users/zube/vscode-distro/out/bootstrap.js:84:18)
	at node_module._resolveLookupPaths (/Users/zube/vscode-distro/out/vs/workbench/api/node/extHostExtensionService.js:23:39)
	at Module._resolveFilename (node:internal/modules/cjs/loader:941:20)
	at o._resolveFilename (node:electron/js2c/utility_process_init:17:848)
	at Module._load (node:internal/modules/cjs/loader:832:27)

on the console at startup in our fork. Adding the Array.isArray() check resolves this issue from throwing the exception. It is also noted that this check is done in a similar block within bootstrap.js so this diff mimics that behavior.