Cannot resolve topic names than are in namespace of other topic

[johuber]

If there is a topic, e.g. /point and another topic called /point/shifted then it's not possible to plot /point/shifted/x because rqt tries to access the element msg.shifted.x of topic /point.

Corresponding warning is:

PlotWidget.update_plot(): error in rosplot: Invalid topic spec [/point/shifted/x]: 'Point' object has no attribute 'shifted'

However, it is possible to add the topic to the list of plotted values (the plus symbol becomes clickable and green) but the curve is not visible afterwards with this warning.

[ahcorde]

This PR ros-visualization/rqt#299 might fix this issue