fix failing initialisation of array with empty braces

include/evalhyd/evald.hpp

@@ -372,7 +372,7 @@ namespace evalhyd
             }
             else
             {
-                return XB3({});
+                return XB3(xt::zeros<bool>({0, 0, 0}));
             }
         };
         const XB3 c_msk = gen_msk();

include/evalhyd/evalp.hpp

@@ -379,7 +379,7 @@ namespace evalhyd
             }
             else
             {
-                return XB4({});
+                return XB4(xt::zeros<bool>({0, 0, 0, 0}));
             }
         };
         const XB4 c_msk = gen_msk();