Reduce indentation in write_data_structures
diff --git a/gen/src/write.rs b/gen/src/write.rs
index 370dac4..dcb7850 100644
--- a/gen/src/write.rs
+++ b/gen/src/write.rs
@@ -119,34 +119,36 @@
         }
     }
 
+    if out.header {
+        return;
+    }
+
     out.set_namespace(Default::default());
 
-    if !out.header {
-        // MSVC workaround for "C linkage function cannot return C++ class" error.
-        // Apparently the compiler fails to perform implicit instantiations as part
-        // of an extern declaration return type. Instead we instantiate explicitly.
-        // See https://stackoverflow.com/a/57429504/6086311.
-        out.next_section();
-        let mut slice_in_return_position = OrderedSet::new();
-        for api in apis {
-            if let Api::CxxFunction(efn) | Api::RustFunction(efn) = api {
-                if let Some(ty @ Type::SliceRef(_)) = &efn.ret {
-                    slice_in_return_position.insert(ty);
-                }
+    // MSVC workaround for "C linkage function cannot return C++ class" error.
+    // Apparently the compiler fails to perform implicit instantiations as part
+    // of an extern declaration return type. Instead we instantiate explicitly.
+    // See https://stackoverflow.com/a/57429504/6086311.
+    out.next_section();
+    let mut slice_in_return_position = OrderedSet::new();
+    for api in apis {
+        if let Api::CxxFunction(efn) | Api::RustFunction(efn) = api {
+            if let Some(ty @ Type::SliceRef(_)) = &efn.ret {
+                slice_in_return_position.insert(ty);
             }
         }
-        for ty in &slice_in_return_position {
-            write!(out, "template class ");
-            write_type(out, ty);
-            writeln!(out, ";");
-        }
+    }
+    for ty in &slice_in_return_position {
+        write!(out, "template class ");
+        write_type(out, ty);
+        writeln!(out, ";");
+    }
 
-        out.next_section();
-        for api in apis {
-            if let Api::TypeAlias(ety) = api {
-                if let Some(reasons) = out.types.required_trivial.get(&ety.name.rust) {
-                    check_trivial_extern_type(out, ety, reasons)
-                }
+    out.next_section();
+    for api in apis {
+        if let Api::TypeAlias(ety) = api {
+            if let Some(reasons) = out.types.required_trivial.get(&ety.name.rust) {
+                check_trivial_extern_type(out, ety, reasons)
             }
         }
     }