Fix crash when deleting a buffer from a user mapping

Deleting a buffer resets normal mode on all clients that were
displaing that buffer, but ScopedForceNormalMode that are used
from user mode  do not take this possiblity into account on
destruction, which leads to deleting the last normal mode from
the context, ending up with an empty mode stack.

Fixes #3909

src/input_handler.cc

@@ -1698,14 +1698,9 @@ InputHandler::ScopedForceNormal::~ScopedForceNormal()
 
     if (m_mode == m_handler.m_mode_stack.back().get())
         m_handler.pop_mode(m_mode);
-    else
-    {
-        auto it = find_if(m_handler.m_mode_stack,
-                          [this](const RefPtr<InputMode>& m)
-                          { return m.get() == m_mode; });
-        kak_assert(it != m_handler.m_mode_stack.end());
+    else if (auto it = find(m_handler.m_mode_stack, m_mode);
+             it != m_handler.m_mode_stack.end())
         m_handler.m_mode_stack.erase(it);
-    }
 }
 
 static bool is_valid(Key key)

src/ref_ptr.hh

@@ -88,8 +88,8 @@ struct RefPtr
         acquire();
     }
 
-    friend bool operator==(const RefPtr& lhs, const RefPtr& rhs) { return lhs.m_ptr == rhs.m_ptr; }
-    friend bool operator!=(const RefPtr& lhs, const RefPtr& rhs) { return lhs.m_ptr != rhs.m_ptr; }
+    friend bool operator==(const RefPtr& lhs, const RefPtr& rhs) = default;
+    friend bool operator==(const RefPtr& lhs, const T* rhs) { return lhs.m_ptr == rhs; }
 
 private:
     T* m_ptr = nullptr;

test/regression/3909-crash-on-closing-buffer-with-user-mapping/cmd

@@ -0,0 +1 @@
+i<a-;>,d<esc>

test/regression/3909-crash-on-closing-buffer-with-user-mapping/in

@@ -0,0 +1 @@
+

test/regression/3909-crash-on-closing-buffer-with-user-mapping/out

@@ -0,0 +1 @@
+

test/regression/3909-crash-on-closing-buffer-with-user-mapping/rc

@@ -0,0 +1,2 @@
+edit -scratch
+map global user d :delete-buffer<ret>