add_ribbons can't handle NA values

The plotly function add_ribbons() doesn't function properly when cases in the middle or at the end have NA values. These lead to a weird behaviour where parts of the ribbons are missing or drawn in wrong places (see Plots 1 & 3). When the connectgaps-Attribute is set to TRUE for the ribbon the bug doesn't appear (see Plot 2).
NA values in the beginning don't seem to be a problem as well (see Plot 3, Red Trace 2).

The same behaviour has also been reported with ggplot and plotly in issue #1060. But because it may either be two separate problems or just a problem in plotly itself also affecting the ggplot visualization I decided to open this separate issue.

R の add_ribbons() 関数から始め、リンクされている Plots 1–3 を使って動作を再現し、中央と末尾の NA 値に重点を置きます。connectgaps を TRUE に設定した場合、および関連する ggplot と plotly の issue #1060 と結果を比較します。connectgaps を必要とせず、ribbons が正しい場所にレンダリングされれば完了です。