rust: rust-project.json: Skip disabled modules

Disabled modules may not have a valid root path.

Bug: 313410568
Test: SOONG_GEN_RUST_PROJECT=1 m nothing
Change-Id: I253cca18493193245aa198adfce5fd75cf27cefb

rust/project_json.go

@@ -119,6 +119,9 @@ func isModuleSupported(ctx android.SingletonContext, module android.Module) (*Mo
 	if !ok {
 		return nil, false
 	}
+	if !rModule.Enabled() {
+		return nil, false
+	}
 	return rModule, true
 }