fix: use env from cachedConfig when offlineEnv is set

This changeset modifies the `dev` command's behavior when the
`--offlineEnv` command is set: Previously, passing `offlineEnv` would
ignore any environment variable data from the cached configuration
file by setting `env` data to an empty object before passing it around.
The unintended consequence of this is that environment variable data
set via the config file is ignored when running Preview Servers.
Environment variable data is not passed to edge functions, and only
build-time variables are passed to functions.

With this change, we'll only default to an empty object when
`cachedConfig.env` is not set. (I don't know if this is a realistic
scenario, but I'm doing it this way to lower the risk of this change.)

Author: ndhoule

src/commands/base-command.ts

@@ -620,10 +620,7 @@ export default class BaseCommand extends Command {
       ...apiUrlOpts,
     })
     const { accounts = [], buildDir, config, configPath, repositoryRoot, siteInfo } = cachedConfig
-    let { env } = cachedConfig
-    if (flags.offlineEnv) {
-      env = {}
-    }
+    const env = cachedConfig?.env ?? {}
     env.NETLIFY_CLI_VERSION = { sources: ['internal'], value: version }
     const normalizedConfig = normalizeConfig(config)