Fix potentially incorrect libid when using save as

If you use save as into a different library and change the symbol name
while overwriting an existing symbol, the libid didn't get updated,
leading to an error message when trying to load the newly saved symbol.

eeschema/symbol_library_manager.cpp

@@ -479,7 +479,11 @@ bool SYMBOL_LIBRARY_MANAGER::UpdateSymbol( LIB_SYMBOL* aSymbol, const wxString&
 
         wxCHECK( bufferedSymbol, false );
 
+        // If we are coming from a different library, the library ID needs to be preserved
+        auto libId = bufferedSymbol->GetLibId();
         *bufferedSymbol = *aSymbol;
+        bufferedSymbol->SetLibId( libId );
+
         symbolBuf->GetScreen()->SetContentModified();
     }
     else                // New symbol