Little improvements

steam_user_stats: Use the value stored in the JSON object.
steal_inventory: use 'empty' that is guaranteed to be constant in time.

dll/steam_inventory.h

@@ -840,7 +840,7 @@ bool SubmitUpdateProperties( SteamInventoryUpdateHandle_t handle, SteamInventory
 
 void RunCallbacks()
 {
-    if (call_definition_update || inventory_requests.size()) {
+    if (call_definition_update || !inventory_requests.empty()) {
         if (!item_definitions_loaded) {
             read_items_db();
             item_definitions_loaded = true;
@@ -854,7 +854,7 @@ void RunCallbacks()
         call_definition_update = false;
     }
 
-    if (inventory_requests.size() && !inventory_loaded) {
+    if (!inventory_requests.empty() && !inventory_loaded) {
         read_inventory_db();
         inventory_loaded = true;
     }

dll/steam_user_stats.h

@@ -350,9 +350,7 @@ const char * GetAchievementDisplayAttribute( const char *pchName, const char *pc
                 return static_cast<std::string const&>(item["name"]) == pchName;
             });
             if (it != defined_achievements.end()) {
-                static std::string display_name;
+                return it.value()["displayName"].get_ptr<std::string*>()->c_str();
-                display_name = it.value()["displayName"].get<std::string>();
-                return display_name.c_str();
             }
         } catch (...) {}
     }
@@ -363,9 +361,7 @@ const char * GetAchievementDisplayAttribute( const char *pchName, const char *pc
                 return static_cast<std::string const&>(item["name"]) == pchName;
             });
             if (it != defined_achievements.end()) {
-                static std::string description;
+                return it.value()["description"].get_ptr<std::string*>()->c_str();
-                description = it.value()["description"].get<std::string>();
-                return description.c_str();
             }
         } catch (...) {}
     }
@@ -376,9 +372,7 @@ const char * GetAchievementDisplayAttribute( const char *pchName, const char *pc
                 return static_cast<std::string const&>(item["name"]) == pchName;
             });
             if (it != defined_achievements.end()) {
-                static std::string hidden;
+                return it.value()["hidden"].get_ptr<std::string*>()->c_str();
-                hidden = it.value()["hidden"].get<std::string>();
-                return hidden.c_str();
             }
         } catch (...) {}
     }