Add missing was_loaded initialization

src/item_category.cpp:30:20: runtime error: load of value 192, which is not a valid value for type 'bool'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior src/item_category.cpp:30:20 in 
src/item_category.cpp:31:19: runtime error: load of value 192, which is not a valid value for type 'bool'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior src/item_category.cpp:31:19 in 
src/item_category.cpp:32:19: runtime error: load of value 192, which is not a valid value for type 'bool'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior src/item_category.cpp:32:19 in

src/item_category.h

@@ -14,7 +14,7 @@ class JsonObject;
 
 // this is a helper struct with rules for picking a zone
 struct zone_priority_data {
-    bool was_loaded;
+    bool was_loaded = false;
     zone_type_id id;
     bool filthy = false;
     cata::flat_set<std::string> flags;