Only create a default *scratch* when we dont have any non debug buffers

Fixes #852
Closes #856

src/buffer_manager.cc

@@ -45,6 +45,9 @@ Buffer* BufferManager::create_buffer(String name, Buffer::Flags flags,
     auto& buffer = *m_buffers.front();
     buffer.on_registered();
 
+    if (contains(m_buffer_trash, &buffer))
+        throw runtime_error("Buffer got removed during its creation");
+
     return &buffer;
 }
 
@@ -82,6 +85,15 @@ Buffer& BufferManager::get_buffer(StringView name)
     return *res;
 }
 
+Buffer& BufferManager::get_first_buffer()
+{
+    if (not contains_that(m_buffers, [](const std::unique_ptr<Buffer>& p)
+                          { return not (p->flags() & Buffer::Flags::Debug); }))
+        create_buffer("*scratch*", Buffer::Flags::None);
+
+    return *m_buffers.front();
+}
+
 void BufferManager::backup_modified_buffers()
 {
     for (auto& buf : m_buffers)

src/buffer_manager.hh

@@ -30,6 +30,8 @@ public:
     Buffer* get_buffer_ifp(StringView name);
     Buffer& get_buffer(StringView name);
 
+    Buffer& get_first_buffer();
+
     void backup_modified_buffers();
 
     void clear_buffer_trash();

src/client_manager.cc

@@ -40,7 +40,7 @@ Client* ClientManager::create_client(std::unique_ptr<UserInterface>&& ui,
                                      EnvVarMap env_vars,
                                      StringView init_commands)
 {
-    Buffer& buffer = **BufferManager::instance().begin();
+    Buffer& buffer = BufferManager::instance().get_first_buffer();
     WindowAndSelections ws = get_free_window(buffer);
     Client* client = new Client{std::move(ui), std::move(ws.window),
                                 std::move(ws.selections), std::move(env_vars),

src/main.cc

@@ -564,17 +564,12 @@ int run_server(StringView session, StringView init_command,
     {
          write_to_debug_buffer(format("error while opening command line files: {}", error.what()));
     }
-    else
-        buffer_manager.create_buffer("*scratch*", Buffer::Flags::None);
 
     try
     {
-        if (not daemon)
-        {
-            local_client = client_manager.create_client(
-                create_local_ui(ui_type), get_env_vars(), init_command);
-
-            if (local_client)
+        if (not daemon and
+            (local_client = client_manager.create_client(
+                 create_local_ui(ui_type), get_env_vars(), init_command)))
         {
             auto& selections = local_client->context().selections_write_only();
             auto& buffer = selections.buffer();
@@ -587,7 +582,6 @@ int run_server(StringView session, StringView init_command,
                     get_face("Error")
                 });
         }
-        }
 
         while (not terminate and (not client_manager.empty() or daemon))
         {