Fix standalone web UI crash when polling player data before ship selection

playerGet() indexed Ship_info with ship_class without bounds checking.
Before ship selection, ship_class is -1, which as an unsigned index
causes an out-of-bounds access. Add the same bounds check that the
Windows standalone GUI already has.

Fixes #7366

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: chief1983

code/network/stand_gui-unix.cpp

@@ -457,7 +457,11 @@ json_t* playerGet(ResourceContext * /*context*/) {
         json_object_set(obj, "host", (MULTI_HOST(p)) ? json_true() : json_false());
         json_object_set(obj, "observer", (MULTI_OBSERVER(p)) ? json_true() : json_false());
         json_object_set(obj, "callsign", json_string(p.m_player->callsign));
-        json_object_set(obj, "ship", json_string(Ship_info[p.p_info.ship_class].name));
+        if (p.p_info.ship_class >= 0 && p.p_info.ship_class < static_cast<int>(Ship_info.size())) {
+            json_object_set(obj, "ship", json_string(Ship_info[p.p_info.ship_class].name));
+        } else {
+            json_object_set(obj, "ship", json_string(""));
+        }
 
         json_array_append(playerList, obj);
     }