Prevent crash from -1 array idx when searching zones

Prevents the crash listed below that previously happened when searching
for zones to add, but the search yielded no results:

```
Thread 1 "cataclysm-tiles" received signal SIGABRT, Aborted.
__pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44

(gdb) bt
 #0  __pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
 #1  0x00007ffff787840f in __pthread_kill_internal (signo=6, threadid=<optimized out>) at ./nptl/pthread_kill.c:78
 #2  0x00007ffff78294f2 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
 #3  0x00007ffff78124ed in __GI_abort () at ./stdlib/abort.c:79
 #4  0x00007ffff7ad501e in std::__glibcxx_assert_fail(char const*, int, char const*, char const*) () from /lib/x86_64-linux-gnu/libstdc++.so.6
 #5  0x0000555555de2639 in std::vector<uilist_entry, std::allocator<uilist_entry> >::operator[] (this=<optimized out>, __n=<optimized out>) at /usr/include/c++/14/bits/stl_vector.h:1130
 #6  std::vector<uilist_entry, std::allocator<uilist_entry> >::operator[] (this=<optimized out>, __n=<optimized out>) at /usr/include/c++/14/bits/stl_vector.h:1128
 #7  0x000055555699deac in uilist_impl::draw_controls (this=0x555599a181d0) at src/ui.cpp:138
 #8  0x0000555555b7c312 in cataimgui::window::draw (this=0x555599a181d0) at src/cata_imgui.cpp:631
 #9  cataimgui::window::draw (this=0x555599a181d0) at src/cata_imgui.cpp:600
 #10 0x00005555569a2b1c in ui_adaptor::redraw_invalidated () at src/ui_manager.cpp:440
 #11 0x00005555569a2bd9 in ui_adaptor::redraw () at src/ui_manager.cpp:345
 #12 0x00005555569a2c00 in ui_manager::redraw () at src/ui_manager.cpp:508
 #13 0x000055555699bfa4 in uilist::inputfilter (this=this@entry=0x7fffffffb9c8) at src/ui.cpp:531
 #14 0x000055555699ead4 in uilist::query (this=this@entry=0x7fffffffb9c8, loop=loop@entry=true, timeout=timeout@entry=-1, allow_unfiltered_hotkeys=allow_unfiltered_hotkeys@entry=false) at src/ui.cpp:865
 #15 0x0000555555c610d4 in zone_manager::query_type (this=this@entry=0x555557274060 <zone_manager::get_manager()::manager>, personal=personal@entry=false) at src/clzones.cpp:621
 #16 0x0000555555ef3894 in game::zones_manager (this=this@entry=0x555558291db0) at src/game.cpp:6944
 #17 0x0000555555f5d279 in game::do_regular_action (this=this@entry=0x555558291db0, act=@0x7fffffffcfec: ACTION_ZONES, player_character=..., mouse_target=std::optional [no contained value]) at src/handle_action.cpp:2438
 #18 0x0000555555f60769 in game::handle_action (this=0x555558291db0) at src/handle_action.cpp:3172
 #19 0x0000555555dcf14d in do_turn () at src/do_turn.cpp:579
 #20 0x00005555557a1217 in main (argc=<optimized out>, argv=<optimized out>) at src/main.cpp:873
```

gdb shows that `parent.selected` was negative:
```
(gdb) frame 7
138                                           parent.entries[parent.selected].desc.c_str()
(gdb) print parent.selected
$1 = -1
(gdb) print parent.entries.size()
$2 = 63
```

src/ui.cpp

@@ -134,9 +134,13 @@ void uilist_impl::draw_controls()
 
     if( parent.desc_enabled ) {
         ImGui::Separator();
-        cataimgui::draw_colored_text( parent.footer_text.empty() ?
-                                      parent.entries[parent.selected].desc.c_str()
-                                      : parent.footer_text.c_str() );
+        std::string description;
+        if( !parent.footer_text.empty() ) {
+            description = parent.footer_text;
+        } else if( parent.selected >= -1 ) {
+            description = parent.entries[parent.selected].desc;
+        }
+        cataimgui::draw_colored_text( description );
     }
 }