remove unnecessary and unused chart debug functionality

Change-Id: Ic8100b2afebe469709723b324394e08b7669d911
make that variable protected again

Change-Id: I17235397e490458c250165c36bec97bf1ce326d7
remove debug output

Change-Id: I7c56adf0cd91f6474145708d91988c974e1ea854
make sure all objects exist, related fdo#75692

fdo75692-2.xlsx and fdo#75692-3.xlsx crash.

Change-Id: I56353e7da1850a49e18d3a570641843600d34b1c
don't try to import invalid document, fdo#79135

Change-Id: I3b601d629550078a8fa353bf838619f8d7b34718
column storage might be changed, related lp#990868

Change-Id: Ibd196484c8c5199e7398726a250082c266a89229