If oldLine is null #updateModifiedServerKey shouldn't be called since it
would derefence it. Spotbugs raised this as problem
RCN_REDUNDANT_NULLCHECK_WOULD_HAVE_BEEN_A_NPE. Fix it by checking if
oldLine is null before calling #updateModifiedServerKey.
Change-Id: I8a2000492986e52ce7dbe25f48b321c05fd371e4
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>