Make graph with one timestamp not look like an empty graph

[shape-warrior-t]

Currently, if the time range for graphing is adjusted so that the time range only includes one telemetry frame, the graph will appear to be empty (likely due to how the lines in the graph are drawn). It's probably better to have, say, a point or something to indicate that there is a (single) piece of data to graph -- in fact, adding explicit dots representing data points in the style of a scatter plot instead of / in addition to lines connecting data points could be a nice change in general.