Fix trying to open undefined certs

The issue is that cfg.get() is returning undefined, which becomes
"undefined".  Originally it was thought cfg.get() would return the
default ("") but it seems that is not always the case.

The trim is an extra addition in case the value is a string with just
whitespace.

src/extension.ts

@@ -38,9 +38,9 @@ export async function activate(ctx: vscode.ExtensionContext): Promise<void> {
   const applyHttpProperties = () => {
     const cfg = vscode.workspace.getConfiguration()
     const insecure = Boolean(cfg.get("coder.insecure"))
-    const certFile = String(cfg.get("coder.tlsCertFile"))
-    const keyFile = String(cfg.get("coder.tlsKeyFile"))
-    const caFile = String(cfg.get("coder.tlsCaFile"))
+    const certFile = String(cfg.get("coder.tlsCertFile") ?? "").trim()
+    const keyFile = String(cfg.get("coder.tlsKeyFile") ?? "").trim()
+    const caFile = String(cfg.get("coder.tlsCaFile") ?? "").trim()
 
     axios.defaults.httpsAgent = new https.Agent({
       cert: certFile === "" ? undefined : fs.readFileSync(certFile),