Rollup merge of #95804 - GuillaumeGomez:empty-doc-comment-with-backline, r=notriddle

rustdoc: Fix empty doc comment with backline ICE

Fixes #95800.

r? ```@notriddle```

src/test/rustdoc/empty-doc-comment.rs

@@ -0,0 +1,22 @@
+// Ensure that empty doc comments don't panic.
+
+/*!
+*/
+
+///
+///
+pub struct Foo;
+
+#[doc = "
+"]
+pub mod Mod {
+   //!
+   //!
+}
+
+/**
+*/
+pub mod Another {
+   #![doc = "
+"]
+}