kmselement: If pad is not created do not try to use it
kmselement: If pad is not created do not try to use it

Change-Id: I7b8ec915ead0a9051ce2c05bf9f0a0cd3ffb7c9c

Kurento/kms-core,Kurento/kms-core,ESTOS/kms-core,ESTOS/kms-core,Kurento/kms-core,ESTOS/kms-core,Kurento/kms-core,ESTOS/kms-core