Bugfix: Fix crash when moving a floating Con to a different workspace, add testcase (Thanks EelVex)

testcases/t/42-regress-move-floating.t

@@ -0,0 +1,19 @@
+#!perl
+# vim:ts=4:sw=4:expandtab
+#
+# Regression: move a floating window to a different workspace crashes i3
+#
+use i3test tests => 1;
+use X11::XCB qw(:all);
+
+my $tmp = get_unused_workspace();
+my $otmp = get_unused_workspace();
+cmd "workspace $tmp";
+
+cmd 'open';
+cmd 'mode toggle';
+cmd "move workspace $otmp";
+
+my $tree = i3('/tmp/nestedcons')->get_tree->recv;
+my @nodes = @{$tree->{nodes}};
+ok(@nodes > 0, 'i3 still lives');