Fix fullscreen focus bug and corresponding test flaw

As the workspace might be reached via recursion (e.g. moving from the edge
of a fullscreen split container), it's necessary to check for a fullscreen
container whenever a workspace is reached.

testcases/t/156-fullscreen-focus.t

@@ -18,7 +18,20 @@
 # the time of launching the new one. Also make sure that focusing containers
 # in other workspaces work even when there is a fullscreen container.
 #
-use i3test;
+use i3test i3_autostart => 0;
+
+# Screen setup looks like this:
+# +----+----+
+# | S1 | S2 |
+# +----+----+
+my $config = <<EOT;
+# i3 config file (v4)
+font -misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1
+
+fake-outputs 1024x768+0+0,1024x768+1024+0
+EOT
+
+my $pid = launch_with_config($config);
 
 my $i3 = i3(get_socket_path());
 
@@ -305,4 +318,6 @@ verify_move(2, 'prevented move to workspace by position');
 
 # TODO: Tests for "move to output" and "move workspace to output".
 
+exit_gracefully($pid);
+
 done_testing;