libwebm: handle (as error) cluster with unknown size
libwebm: handle (as error) cluster with unknown size

Change-Id: I8342d50d0482d77cb895ae659568016eb48ed2be

webmproject/libwebm,felipebetancur/libwebm,Acidburn0zzz/webm.libwebm,felipebetancur/libwebm,ericmckean/webm.libwebm,jdm/libwebm,gshORTON/webm.libwebm,webmproject/libwebm,kalli123/webm.libwebm,zofuthan/libwebm,Suvarna1488/webm.libwebm,webmproject/libwebm,kim42083/webm.libwebm,iniwf/webm.libwebm,matanbs/webm.libwebm,reimaginemedia/webm.libwebm,zofuthan/libwebm,Maria1099/webm.libwebm,abwiz0086/webm.libwebm,pcwalton/libwebm,kleopatra999/webm.libwebm