qmetatype.cpp: provide missing initializer for const variable

qmetatype.cpp(1565): warning #854: const variable "metatypeHelper" requires an initializer -- class "struct <unnamed>" has no user-provided default constructor

Change-Id: I2bbf422288924c198645fffd16a9b868ff7adcb9
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/kernel/qmetatype.cpp

@@ -1524,7 +1524,7 @@ static const struct : QMetaTypeModuleHelper
         }
         return false;
     }
-} metatypeHelper;
+} metatypeHelper = {};
 
 static const QMetaTypeModuleHelper *qMetaTypeCoreHelper = &metatypeHelper;
 Q_CORE_EXPORT const QMetaTypeModuleHelper *qMetaTypeGuiHelper = nullptr;