Fix crash and empty action in SUI Actions Page (#11427)

## Summary of the Pull Request
Fixes two issues related to SUI's Actions page:
1. Crash when adding an action and setting key chord to one that is already taken
   - **Cause**: the new key binding that was introduced with the "Add new" button appears in `_KeyBindingList` that we're iterating over. This has no `CurrentKeys()`, resulting in a null pointer exception.
   - **Fix**: null-check it
2. There's an action that appears as being nameless in the dropdown
   - **Cause**: The culprit seems to be `MultipleActions`. We would register it, but it wouldn't have a name, so it would appear as a nameless option.
   - **Fix**: if it has no name, don't register it. This is also future-proof in that any new nameless actions won't be automatically added.

Closes #10981
Part of #11353

src/cascadia/TerminalSettingsEditor/Actions.cpp

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation.
+// Copyright (c) Microsoft Corporation.
 // Licensed under the MIT license.
 
 #include "pch.h"
@@ -369,7 +369,7 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         {
             const auto kbdVM{ get_self<KeyBindingViewModel>(_KeyBindingList.GetAt(i)) };
             const auto& otherKeys{ kbdVM->CurrentKeys() };
-            if (keys.Modifiers() == otherKeys.Modifiers() && keys.Vkey() == otherKeys.Vkey())
+            if (otherKeys && keys.Modifiers() == otherKeys.Modifiers() && keys.Vkey() == otherKeys.Vkey())
             {
                 return i;
             }

src/cascadia/TerminalSettingsModel/ActionMap.cpp

@@ -94,15 +94,14 @@ namespace winrt::Microsoft::Terminal::Settings::Model::implementation
     static void RegisterShortcutAction(ShortcutAction shortcutAction, std::unordered_map<hstring, Model::ActionAndArgs>& list, std::unordered_set<InternalActionID>& visited)
     {
         const auto actionAndArgs{ make_self<ActionAndArgs>(shortcutAction) };
-        if (actionAndArgs->Action() != ShortcutAction::Invalid)
+        /*We have a valid action.*/
+        /*Check if the action was already added.*/
+        if (visited.find(Hash(*actionAndArgs)) == visited.end())
         {
-            /*We have a valid action.*/
-            /*Check if the action was already added.*/
-            if (visited.find(Hash(*actionAndArgs)) == visited.end())
+            /*This is an action that wasn't added!*/
+            /*Let's add it if it has a name.*/
+            if (const auto name{ actionAndArgs->GenerateName() }; !name.empty())
             {
-                /*This is an action that wasn't added!*/
-                /*Let's add it.*/
-                const auto name{ actionAndArgs->GenerateName() };
                 list.insert({ name, *actionAndArgs });
             }
         }