Handle Faraday errors

app/models/execution_environment.rb

@@ -51,6 +51,9 @@ class ExecutionEnvironment < ApplicationRecord
 
     Rails.logger.warn("Could not create execution environment in Poseidon, got response: #{response.as_json}")
     false
+  rescue Faraday::Error => e
+    Rails.logger.warn("Could not create execution environment because of Faraday error: #{e.inspect}")
+    false
   end
 
   def to_json(*_args)

app/models/submission.rb

@@ -197,7 +197,7 @@ class Submission < ApplicationRecord
     runner = Runner.for(user, exercise)
     copy_files_to runner
     waiting_duration = Time.zone.now - request_time
-    yield(runner, waiting_duration) if block_given?
+    yield(runner, waiting_duration)
   end
 
   def command_for(template, file)