windows: fix maximize button with OS titlebar

refs: #3499

docs/changelog.md

@@ -39,6 +39,8 @@ As features stabilize some brief notes about them will accumulate here.
   terminal. #3529.
 * tab width calculation when returning a string with embedded escape
   sequences from a `format-tab-title` event handler. #3481
+* Windows: clicking the maximize button didn't work unless using
+  integrated titlebar buttons. #3499
 
 ### 20230408-112425-69ae8472
 

window/src/os/windows/window.rs

@@ -1586,6 +1586,14 @@ unsafe fn nc_mouse_button(
     lparam: LPARAM,
 ) -> Option<LRESULT> {
     let inner = rc_from_hwnd(hwnd)?;
+
+    let no_native_title_bar = no_native_title_bar(inner.borrow().config.window_decorations);
+    if !no_native_title_bar {
+        // Don't mess with this event unless we're doing our own custom
+        // titlebar
+        return None;
+    }
+
     // To support dragging the window, capture when the left
     // button goes down and release when it goes up.
     // Without this, the drag state can be confused when dragging