QNativeIpcKey: make isEmpty() and isValid() noexcept

They have no preconditions and cannot throw.

Change-Id: I9c3020e00cffc84dfc3a14469cbb80557a4df5cf
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
(cherry picked from commit ba95594ea211a045f0e28326a066917a662c89db)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/ipc/qtipccommon.h

@@ -85,12 +85,12 @@ public:
         key.swap(other.key);
     }
 
-    bool isEmpty() const
+    bool isEmpty() const noexcept
     {
         return key.isEmpty();
     }
 
-    bool isValid() const
+    bool isValid() const noexcept
     {
         return type() != Type{};
     }