throw more useful exception from OPropertySetHelper::getPropertyValue

Change-Id: I90e7ab5763bf368cec795a8c39ece17579dd851d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/172905
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Jenkins

cppuhelper/source/propshlp.cxx

@@ -273,6 +273,8 @@ Any OPropertySetHelper::getPropertyValue(
     IPropertyArrayHelper & rPH = getInfoHelper();
     // map the name to the handle
     sal_Int32 nHandle = rPH.getHandleByName( rPropertyName );
+    if (nHandle == -1)
+        throw UnknownPropertyException(rPropertyName);
     // call the method of the XFastPropertySet interface
     return getFastPropertyValue( nHandle );
 }
@@ -545,8 +547,8 @@ void OPropertySetHelper::setFastPropertyValue( sal_Int32 nHandle, const Any& rVa
 
 // XFastPropertySet
 Any OPropertySetHelper::getFastPropertyValue( sal_Int32 nHandle )
-
 {
+    assert(nHandle != -1 && "passing -1 here indicates that the caller knows this is not a valid handle");
     IPropertyArrayHelper & rInfo = getInfoHelper();
     if( !rInfo.fillPropertyMembersByHandle( nullptr, nullptr, nHandle ) )
         // unknown property