Guard against non-json that looks like json (#1736)

* Guard against non-json that looks like json

* Filter out empty spans on client, so server doesn't throw

Author: myieye

backend/FwLite/LcmCrdt/LcmCrdtDbContext.cs

@@ -56,7 +56,13 @@ private class RichStringDbConverter() : ValueConverter<RichString?, string?>(
         {
             if (maybeJson is null) return null;
             if (maybeJson.StartsWith('[') || maybeJson.StartsWith('{'))
-                return JsonSerializer.Deserialize<RichString?>(maybeJson);
+            {
+                try
+                {
+                    return JsonSerializer.Deserialize<RichString?>(maybeJson);
+                }
+                catch { }
+            }
             return new RichString(maybeJson);
         }
     }

frontend/viewer/src/lib/components/lcm-rich-text-editor/lcm-rich-text-editor.svelte

@@ -79,7 +79,8 @@
           //todo, eventually we might want to let the user edit span props, not sure if node attributes or marks are the correct way to handle that
           //I suspect marks is the right way though.
           if (!value) value = {spans: []};
-          value.spans = newState.doc.children.map((child) => richSpanFromNode(child));
+          value.spans = newState.doc.children.map((child) => richSpanFromNode(child))
+            .filter(s => s.text);
           dirty = true;
         }
         editor.updateState(newState);