Fix database library symbols disappearing in symbol chooser

The GetLibraryStatus() check was only verifying that the optional had a
value, not that the library was actually loaded. Database libraries return
a status even when not fully loaded, causing them to be skipped during
tree population.

Check both that the status exists AND that load_status is LOADED before
considering a library as ready for display.

Additionally, we need to clear the HTML placeholders when loading fails
to prevent them leaking

Fixes https://gitlab.com/kicad/code/kicad/-/issues/16667

eeschema/generate_alias_info.cpp

@@ -66,7 +66,10 @@ public:
         wxCHECK_RET( m_libs, "Symbol library manager adapter pointer is not valid" );
 
         if( !m_lib_id.IsValid() )
+        {
+            ClearPlaceholders();
             return;
+        }
 
         try
         {
@@ -78,6 +81,7 @@ public:
                         m_lib_id.GetLibItemName().wx_str(),
                         m_lib_id.GetLibNickname().wx_str(),
                         ioe.What() );
+            ClearPlaceholders();
             return;
         }
 
@@ -89,6 +93,10 @@ public:
             SetHtmlKeywords();
             SetHtmlFieldTable();
         }
+        else
+        {
+            ClearPlaceholders();
+        }
     }
 
     /**
@@ -253,6 +261,15 @@ protected:
         m_html.Replace( wxS( "__FIELDS__" ), fieldtable );
     }
 
+    void ClearPlaceholders()
+    {
+        m_html.Replace( wxS( "__NAME__" ), wxEmptyString );
+        m_html.Replace( wxS( "__ALIASOF__" ), wxEmptyString );
+        m_html.Replace( wxS( "__DESC__" ), wxEmptyString );
+        m_html.Replace( wxS( "__KEY__" ), wxEmptyString );
+        m_html.Replace( wxS( "__FIELDS__" ), wxEmptyString );
+    }
+
 private:
     wxString                        m_html;
     SYMBOL_LIBRARY_ADAPTER* m_libs;

eeschema/symbol_tree_model_adapter.cpp

@@ -120,7 +120,9 @@ void SYMBOL_TREE_MODEL_ADAPTER::AddLibraries( SCH_BASE_FRAME* aFrame )
 
     for( const wxString& lib : toLoad )
     {
-        if( !m_adapter->GetLibraryStatus( lib ) )
+        std::optional<LIB_STATUS> status = m_adapter->GetLibraryStatus( lib );
+
+        if( !status || status->load_status != LOAD_STATUS::LOADED )
         {
             m_pending_load_libraries.insert( lib );
             continue;