histogram filtering issues

[tmazor]

Not sure if these are related or independent bugs, but I found the following issues when applying filters based on mutation count histogram in msk_impact_2017:

1. filtering to a single bar of the historgram (eg mutation count = 8), fails - the page goes blank and this is in the console:
   
   Filtering to a single bar on other histograms works just fine, so I suspect this is because each bar of the mutation count histogram is not a range but a single value.

2. If I select the >14 bar, the histogram highlights both the 14 & >14 bars
   
   I think the filter that gets applied is correct (header is right and when I browsed Clinical Data tab, all counts were 15+), but the histogram is misleading.
   I don't see this happening with other histograms, so I suspect this is again related to the fact that each bar here is a single value.

[inodb]

Added second issue to separate ticket (#9173)