Wrong current index row

[jdujava]

The current index row selection implemented in #561 is flawed. Consider following scenario:

Index

1  First Section
  1.1  Subsection One
  1.2  Subsection Two
2  Second Section

Scrolling the document right before 2 Second Section, the "current index row" is then chosen as 1 First Section.

[jdujava]

Implementation in #614 has still problems to descend to higher depths on one try for some reason. In the following example, placed on Subsection 1.1.1 in document, with totally collapsed index, on the first opening the selection jumps to 1.1, and only on second toggle to 1.1.1.

1  First Section
  1.1  Subsection One
    1.1.1 Subsubsection
  1.2  Subsection Two
2  Second Section