Handle no devenv situations gracefully

app.ts

@@ -24,18 +24,26 @@ switch (Deno.args[0]) {
 
 const snuff = await sniff(Path.cwd());
 
+if (snuff.pkgs.length === 0 && Object.keys(snuff.env).length === 0) {
+  console.error("no devenv detected");
+  Deno.exit(1);
+}
+
+let env = '';
 const pkgspecs = snuff.pkgs.map((pkg) => `+${utils.pkg.str(pkg)}`);
 
-const cmd = new Deno.Command("pkgx", {
-  args: [...pkgspecs],
-  stdout: "piped",
-  env: { CLICOLOR_FORCE: "1" }, // unfortunate
-}).spawn();
+if (snuff.pkgs.length > 0) {
+  const cmd = new Deno.Command("pkgx", {
+    args: [...pkgspecs],
+    stdout: "piped",
+    env: { CLICOLOR_FORCE: "1" }, // unfortunate
+  }).spawn();
 
-await cmd.status;
+  await cmd.status;
 
-const stdout = (await cmd.output()).stdout;
-let env = new TextDecoder().decode(stdout);
+  const stdout = (await cmd.output()).stdout;
+  env = new TextDecoder().decode(stdout);
+}
 
 // add any additional env that we sniffed
 for (const [key, value] of Object.entries(snuff.env)) {
@@ -46,8 +54,11 @@ env = env.trim();
 
 let undo = "";
 for (const envln of env.trim().split("\n")) {
+  if (!envln) continue;
+
   const [key] = envln.split("=", 2);
   const value = Deno.env.get(key);
+
   if (value) {
     undo += `    export ${key}=${shell_escape(value)}\n`;
   } else {