Input: Do not grab focus from active window

This is essentially the same as 53fa4c7, but for `XGrabKeyboard`, not just `XGrabButton`. See that commit for details

ref phil294/vimium-everywhere#3

src/cmd/x11/window/win-util.cr

@@ -16,7 +16,7 @@ class Cmd::X11::Window::Util
 				wid = title[7..].to_u64?
 				raise Run::RuntimeException.new "ahk_id must be a number" if ! wid
 				win = XDo::Window.new(thread.runner.display.x_do.xdo_p, wid)
-    			win = nil if ! win.name
+    			win = nil if ! win.name # avoids segfaults
 			else
 				text = match_conditions[1]? || ""
 				exclude_title = match_conditions[2]? || ""

src/run/display/x11.cr

@@ -336,10 +336,9 @@ module Run
 			end
 			@mutex.unlock
 		end
-		# TODO: retest, also BlockInput command
 		def grab_keyboard
 			@mutex.lock
-			@display.grab_keyboard(grab_window: @root_win, owner_events: true, pointer_mode: ::X11::GrabModeAsync, keyboard_mode: ::X11::GrabModeAsync, time: ::X11::CurrentTime)
+			@display.grab_keyboard(grab_window: @last_active_window, owner_events: true, pointer_mode: ::X11::GrabModeAsync, keyboard_mode: ::X11::GrabModeAsync, time: ::X11::CurrentTime)
 			@mutex.unlock
 		end
 		def ungrab_keyboard