libs/kaptan-mavlink: fix invalid dialect bug

Signed-off-by: Onur Özkan <work@onurozkan.dev>

libs/kaptan-mavlink/build.rs

@@ -6,6 +6,7 @@ fn main() {
     let manifest_directory = PathBuf::from(std::env::var("CARGO_MANIFEST_DIR").unwrap());
     let dialect = manifest_directory.join("definitions/kaptan.xml");
     let output_directory = std::env::var("OUT_DIR").unwrap();
+    let dialect_source = std::fs::read_to_string(&dialect).unwrap();
     let generated = mavlink_bindgen::generate(
         mavlink_bindgen::XmlDefinitions::Files(vec![dialect]),
         output_directory,
@@ -13,4 +14,8 @@ fn main() {
     .unwrap();
 
     mavlink_bindgen::emit_cargo_build_messages(&generated);
+    println!("cargo::rustc-check-cfg=cfg(kaptan_has_messages)");
+    if dialect_source.contains("<message ") {
+        println!("cargo::rustc-cfg=kaptan_has_messages");
+    }
 }