The create_plot_info_new() function releases old plot data. This
can only work if the plot_info structure was initialized previously.
The ProfileWidget2 did that by a memset, but other parts of the code
did not.
Therefore, introduce a init_plot_info() function and call that when
generating a plot_info struct. Constructors would make this so much
easier - but since this is called from C, we can't use them.
Fixes#2251
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
25b30da244