Fixed bug: with plot tool, when pressing mouse down and immediately
dragging then, it is possible that certaing shared fields aren't
initialized properly due to the operations using those shared fields
aren't synchronized properly and null reference expections can occur.

Now, these operations are synchronized properly (as tests indicate so
far) for plot tool.

Signed-off-by: Jakob Brandsborg Ehmsen <jakobehmsen.github@gmail.com>