Fix typo

Change-Id: I4cfc98ab3be0c789274978ec6b26f981ad627494
Reviewed-on: https://gerrit.libreoffice.org/73634
Tested-by: Jenkins
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>

include/cppuhelper/propshlp.hxx

@@ -546,7 +546,7 @@ protected:
 
     /**
        Converted the value rValue and return the result in rConvertedValue and the
-       old value in rOldValue. A IllegalArgumentException is thrown.
+       old value in rOldValue. An IllegalArgumentException is thrown.
        The method is not implemented in this class. After this call the vetoable
        listeners are notified.