Handle GetForegroundWindow() returning NULL.

anntzer · anntzer · commit 0097b024305c · 2024-05-21T19:05:05.000+02:00
GetForegroundWindow() is documented as sometimes returning NULL, which
is not a valid argument to PyCapsule_New.  Use None to cover that case,
instead.
diff --git a/lib/matplotlib/backends/_backend_tk.py b/lib/matplotlib/backends/_backend_tk.py
@@ -44,7 +44,7 @@ def _restore_foreground_window_at_end():
     try:
         yield
     finally:
-        if mpl.rcParams['tk.window_focus']:
+        if foreground and mpl.rcParams['tk.window_focus']:
             _c_internal_utils.Win32_SetForegroundWindow(foreground)
 
 
diff --git a/src/_c_internal_utils.cpp b/src/_c_internal_utils.cpp
@@ -111,7 +111,11 @@ static py::object
 mpl_GetForegroundWindow(void)
 {
 #ifdef _WIN32
-  return py::capsule(GetForegroundWindow(), "HWND");
+  if (HWND hwnd = GetForegroundWindow()) {
+    return py::capsule(hwnd, "HWND");
+  } else {
+    return py::none();
+  }
 #else
   return py::none();
 #endif
