fix: skip_lines/skip_bytes filters producing empty output on large files

FilteringReader::read() returned Ok(0) (EOF) when a filter consumed a
chunk without producing output. Filters like skip_lines need to see
multiple chunks before outputting anything — returning 0 prematurely
truncated the stream. Loop until the filter produces output or the
underlying reader is truly exhausted.

src/services/item_service.rs

@@ -812,16 +812,19 @@ impl<R: Read> Read for FilteringReader<R> {
             return self.reader.read(buf);
         }
 
-        // Read from the original reader into the reusable temp buffer
-        let to_read = std::cmp::min(buf.len(), self.temp_buf.len());
-        let bytes_read = self.reader.read(&mut self.temp_buf[..to_read])?;
+        // Read chunks and process through the filter chain.
+        // Loop because filters like skip_lines may consume entire chunks
+        // without producing output — that is not EOF, we must keep reading.
+        let chain = self.filter_chain.as_mut().unwrap();
+        loop {
+            let to_read = std::cmp::min(buf.len(), self.temp_buf.len());
+            let bytes_read = self.reader.read(&mut self.temp_buf[..to_read])?;
 
-        if bytes_read == 0 {
-            return Ok(0);
-        }
+            if bytes_read == 0 {
+                // True EOF from the underlying reader
+                return Ok(0);
+            }
 
-        // Process through the filter chain
-        if let Some(ref mut chain) = self.filter_chain {
             let mut input_cursor = std::io::Cursor::new(&self.temp_buf[..bytes_read]);
             chain.filter(&mut input_cursor, &mut self.buffer)?;
 
@@ -829,13 +832,9 @@ impl<R: Read> Read for FilteringReader<R> {
                 let bytes_to_copy = std::cmp::min(buf.len(), self.buffer.len());
                 buf[..bytes_to_copy].copy_from_slice(&self.buffer[..bytes_to_copy]);
                 self.buffer_pos = bytes_to_copy;
-                Ok(bytes_to_copy)
-            } else {
-                // No data produced by filter, signal to read more
-                Ok(0)
+                return Ok(bytes_to_copy);
             }
-        } else {
-            unreachable!()
+            // Filter produced no output for this chunk — read another
         }
     }
 }