replace comma for semi-colon option not disabled for DAS sources in sequence fetcher

The formal specification for das sources says that any landmark used to query a source may be appended with a :X,Y where X,Y specifies a range on the landmark being queried. The switch controlling the autoreplace of commas for semicolons (JAL-657) should be automatically greyed out when DAS sources are selected for retrieval, but in v2.7 this is only the case if the test query includes a comma.