fix projection pushdown index mapping

Author: 0xcaff

packages/duckdb_protobuf/src/read.rs

@@ -17,14 +17,14 @@ pub fn write_to_output(
 ) -> Result<(), anyhow::Error> {
     let column_key = &ColumnKey::empty();
     let fields = value.descriptor().fields().collect::<Vec<_>>();
-    for field_idx in mappings {
+    for (output_field_idx, field_idx) in mappings.iter().enumerate() {
         let field_idx = *field_idx as usize;
         if field_idx >= fields.len() {
             continue;
         }
 
         let field_descriptor = &fields[field_idx];
-        let column_vector = output.get_vector(field_idx);
+        let column_vector = output.get_vector(output_field_idx);
         let value = value.get_field(&field_descriptor);
 
         let column_key = column_key.field(&field_descriptor);