fix bug when no data in peer plotting widget

closes #232 (closed)

Use new attr has_data to help not processing the peer plotting widget if it has no data to avoid the case the ruler or zoommarker haven not been created yet.

requested review from @kienle

assigned to @ldam

requested review from @kienle

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approved this merge request

added 17 commits

• 99563a13...870c04dc - 16 commits from branch develop
• bb514996 - Merge branch 'develop' into i232_fix_bug_when_nodata_in_peer_plotting_widget

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reset approvals from @kienle by pushing to the branch

added 3 commits

• bb514996...11a78e81 - 2 commits from branch develop
• 860e97c2 - Merge branch 'develop' into i232_fix_bug_when_nodata_in_peer_plotting_widget

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changed the description

merged

mentioned in commit 2c1249be