fix: correct type mismatch in max_buffer_size handling

Co-authored-by: aider (openai/andrew/openrouter/qwen/qwen3-coder) <aider@aider.chat>

src/meta_plugin/magic.rs

@@ -165,7 +165,7 @@ impl MetaPlugin for MagicFileMetaPlugin {
         }
         
         if let Some(max_buffer_size) = options.get("max_buffer_size") {
-            if let Ok(size) = max_buffer_size.as_u64() {
+            if let Some(size) = max_buffer_size.as_u64() {
                 self.max_buffer_size = size as usize;
             }
         }