Fix panic with empty attribute inner comment (#6332)

Fixes https://github.com/astral-sh/ruff/issues/6181

crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/attribute.py

@@ -106,4 +106,6 @@ x6 = (
     a.b
 )
 
-
+# regression: https://github.com/astral-sh/ruff/issues/6181
+(#
+()).a

crates/ruff_python_formatter/src/comments/placement.rs

@@ -998,10 +998,14 @@ fn handle_attribute_comment<'a>(
     comment: DecoratedComment<'a>,
     attribute: &'a ast::ExprAttribute,
 ) -> CommentPlacement<'a> {
-    debug_assert!(
-        comment.preceding_node().is_some(),
-        "The enclosing node an attribute expression, expected to be at least after the name"
-    );
+    if comment.preceding_node().is_none() {
+        // ```text
+        // (    value)   .   attr
+        //  ^^^^ we're in this range
+        // ```
+
+        return CommentPlacement::leading(attribute.value.as_ref(), comment);
+    }
 
     // ```text
     // value   .   attr

crates/ruff_python_formatter/tests/snapshots/format@expression__attribute.py.snap

@@ -112,7 +112,9 @@ x6 = (
     a.b
 )
 
-
+# regression: https://github.com/astral-sh/ruff/issues/6181
+(#
+()).a
 ```
 
 ## Output
@@ -200,6 +202,12 @@ x6 = (
     # Check assumption with enclosing nodes
     a.b
 )
+
+# regression: https://github.com/astral-sh/ruff/issues/6181
+(
+    #
+    ()
+).a
 ```