Fix parentheses-equality warning
This fixes a warning when compiling with Clang 17:
thunar-window.c:2144:21: warning: equality comparison with extraneous parentheses [-Wparentheses-equality]
2144 | if ((window->view == new_view))
| ~~~~~~~~~~~~~^~~~~~~~~~~
thunar-window.c:2144:21: note: remove extraneous parentheses around the comparison to silence this warning
2144 | if ((window->view == new_view))
| ~ ^ ~
thunar-window.c:2144:21: note: use '=' to turn this equality comparison into an assignment
2144 | if ((window->view == new_view))
| ^~
| =
1 warning generated.