Minor fixes for layout and workspace

* exwm-layout.el (exwm-layout-show-mode-line): Force update mode-line.

* exwm-workspace.el (exwm-workspace--update-minibuffer): Treat nil as empty
string.

exwm-layout.el

@@ -455,7 +455,8 @@ See also `exwm-layout-enlarge-window'."
                            (window-mode-line-height (frame-root-window
                                                      exwm--floating-frame)))
                         nil t)
-      (exwm-input-grab-keyboard))))
+      (exwm-input-grab-keyboard))
+    (force-mode-line-update)))
 
 ;;;###autoload
 (defun exwm-layout-toggle-mode-line ()

exwm-workspace.el

@@ -453,7 +453,7 @@ The optional FORCE option is for internal use only."
                               (setq result
                                     (+ result
                                        (ceiling (1+ (length i)) width))))
-                            (split-string (current-message) "\n"))
+                            (split-string (or (current-message) "") "\n"))
                       result)
                   (count-screen-lines))))))
     (when (and (integerp max-mini-window-height)