On X11, don't require XIM to be present

In general, we may want to use xinput v2 for keyboard input in such
cases, so we have compose going, but for now just don't crash if
there's no XIM.

src/platform_impl/linux/x11/window.rs

@@ -555,9 +555,9 @@ impl UnownedWindow {
             leap!(xconn.select_xinput_events(window.xwindow, super::ALL_MASTER_DEVICES, mask))
                 .ignore_error();
 
-            {
-                let result = event_loop
-                    .ime
+            // Try to create input context for the window.
+            if let Some(ime) = event_loop.ime.as_ref() {
+                let result = ime
                     .borrow_mut()
                     .create_context(window.xwindow as ffi::Window, false);
                 leap!(result);