QNativeIpcKey: make isEmpty() and isValid() noexcept

They have no preconditions and cannot throw.

Pick-to: 6.6
Change-Id: I9c3020e00cffc84dfc3a14469cbb80557a4df5cf
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

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{};
     }