Add checks for Dotenv before calling it

`composer install --no-dev` fails when Dotenv is a dev dependency (which
it is in skeleton) and you're running in an environment without an
APP_ENV variable set.

Throw exception when no env variables are set and Dotenv is absent so
the user knows to either require DotEnv or specify an APP_ENV variable.

behat/symfony2-extension/2.1/features/bootstrap/bootstrap.php

@@ -4,5 +4,8 @@ use Symfony\Component\Dotenv\Dotenv;
 
 // The check is to ensure we don't use .env in production
 if (!isset($_SERVER['APP_ENV'])) {
+    if (!class_exists(Dotenv::class)) {
+        throw new \RuntimeException('APP_ENV environment variable is not defined. You need to define environment variables for configuration or add "symfony/dotenv" as a Composer dependency to load variables from a .env file.');
+    }
     (new Dotenv())->load(__DIR__.'/../../.env');
 }

symfony/console/3.3/bin/console

@@ -16,6 +16,9 @@ if (!class_exists(Application::class)) {
 }
 
 if (!isset($_SERVER['APP_ENV'])) {
+    if (!class_exists(Dotenv::class)) {
+        throw new \RuntimeException('APP_ENV environment variable is not defined. You need to define environment variables for configuration or add "symfony/dotenv" as a Composer dependency to load variables from a .env file.');
+    }
     (new Dotenv())->load(__DIR__.'/../.env');
 }
 

symfony/framework-bundle/3.3/public/index.php

@@ -9,6 +9,9 @@ require __DIR__.'/../vendor/autoload.php';
 
 // The check is to ensure we don't use .env in production
 if (!isset($_SERVER['APP_ENV'])) {
+    if (!class_exists(Dotenv::class)) {
+        throw new \RuntimeException('APP_ENV environment variable is not defined. You need to define environment variables for configuration or add "symfony/dotenv" as a Composer dependency to load variables from a .env file.');
+    }
     (new Dotenv())->load(__DIR__.'/../.env');
 }