parser: Fix handling of #[path] attributes inside inline submodules.

As seen in hashbrown:

    #[cfg(feature = "raw")]
    /// Experimental and unsafe `RawTable` API. This module is only available if the
    /// `raw` feature is enabled.
    pub mod raw {
        // The RawTable API is still experimental and is not properly documented yet.
        #[allow(missing_docs)]
        #[path = "mod.rs"]
        mod inner;
        pub use inner::*;

        #[cfg(feature = "rayon")]
        pub mod rayon {
            pub use crate::external_trait_impls::rayon::raw::*;
        }
    }

tests/rust/mod_2015/src/nested/mod.rs

@@ -1 +1,6 @@
 pub mod other;
+
+mod other3 {
+    #[path = "other4.rs"]
+    mod other4;
+}

tests/rust/mod_2015/src/nested/other3/other4.rs

@@ -0,0 +1,2 @@
+#[no_mangle]
+pub unsafe extern "C" fn from_really_nested_mod() { }

tests/rust/mod_2018/src/nested.rs

@@ -2,3 +2,8 @@ pub mod other;
 
 #[path = "other2.rs"]
 pub mod other2;
+
+pub mod other3 {
+    #[path = "other4.rs"]
+    pub mod other4;
+}

tests/rust/mod_2018/src/nested/other3/other4.rs

@@ -0,0 +1,2 @@
+#[no_mangle]
+pub unsafe extern "C" fn from_really_nested_mod() { }