fix: pass double ptr to result_from_duckdb_appender

this ensures that the pointer is correctly cleared when errors occur

src/appender/arrow.rs

@@ -39,7 +39,7 @@ impl Appender<'_> {
         record_batch_to_duckdb_data_chunk(&record_batch, &mut data_chunk).map_err(|_op| Error::AppendError)?;
 
         let rc = unsafe { duckdb_append_data_chunk(self.app, data_chunk.get_ptr()) };
-        result_from_duckdb_appender(rc, self.app)
+        result_from_duckdb_appender(rc, &mut self.app)
     }
 }
 

src/appender/mod.rs

@@ -67,7 +67,7 @@ impl Appender<'_> {
         params.__bind_in(self)?;
         // NOTE: we only check end_row return value
         let rc = unsafe { ffi::duckdb_appender_end_row(self.app) };
-        result_from_duckdb_appender(rc, self.app)
+        result_from_duckdb_appender(rc, &mut self.app)
     }
 
     #[inline]
@@ -145,7 +145,7 @@ impl Appender<'_> {
     pub fn flush(&mut self) -> Result<()> {
         unsafe {
             let res = ffi::duckdb_appender_flush(self.app);
-            result_from_duckdb_appender(res, self.app)
+            result_from_duckdb_appender(res, &mut self.app)
         }
     }
 }

src/error.rs

@@ -225,17 +225,17 @@ fn error_from_duckdb_code(code: ffi::duckdb_state, message: Option<String>) -> R
 
 #[cold]
 #[inline]
-pub fn result_from_duckdb_appender(code: ffi::duckdb_state, mut appender: ffi::duckdb_appender) -> Result<()> {
+pub fn result_from_duckdb_appender(code: ffi::duckdb_state, appender: *mut ffi::duckdb_appender) -> Result<()> {
     if code == ffi::DuckDBSuccess {
         return Ok(());
     }
     unsafe {
-        let message = if appender.is_null() {
+        let message = if (*appender).is_null() {
             Some("appender is null".to_string())
         } else {
-            let c_err = ffi::duckdb_appender_error(appender);
+            let c_err = ffi::duckdb_appender_error(*appender);
             let message = Some(CStr::from_ptr(c_err).to_string_lossy().to_string());
-            ffi::duckdb_appender_destroy(&mut appender);
+            ffi::duckdb_appender_destroy(appender);
             message
         };
         error_from_duckdb_code(code, message)

src/inner_connection.rs

@@ -102,7 +102,7 @@ impl InnerConnection {
                 &mut c_app,
             )
         };
-        result_from_duckdb_appender(r, c_app)?;
+        result_from_duckdb_appender(r, &mut c_app)?;
         Ok(Appender::new(conn, c_app))
     }