visulizer: fix exception with empty input
visulizer: fix exception with empty input

cdglabs/ohm,coopsource/ohm,anfedorov/ohm,cdglabs/ohm,DanielTomlinson/ohm,harc/ohm,harc/ohm,DanielTomlinson/ohm,coopsource/ohm,cdglabs/ohm,anfedorov/ohm,coopsource/ohm,DanielTomlinson/ohm,anfedorov/ohm,harc/ohm