llama : fix try_override for bool_value which always return true (#4519)

Author: hankcs

llama.cpp

@@ -1937,7 +1937,7 @@ namespace GGUFMeta {
                 target = override->bool_value;
                 return true;
             }
-            return true;
+            return false;
         }
 
         template<typename OT>