Fix bug that acquires attribute chan on ax on the non plotting area

closes #119 (closed)

Solving by checking if user is clicking on plotting area before getting chan attribute of ax.

assigned to @ldam

approved this merge request

added 7 commits

• 5dacf553...7fbffec8 - 6 commits from branch master
• bf237e5d - Merge branch 'master' into i119_bug_ax_no_chan_on_pick_event

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merged

mentioned in commit 51a64c4d