Volpiano search results mishandle missing music

In the process of looking into #647, I uncovered another issue with volpiano search, which seems to be unrelated.

When displaying volpiano search results, Cantus Ultimus aligns the standardized text with the volpiano melody.

So, for example, this chant:

shows up like this:

This seems generally fine, except does cause some errors. For example, in this chant, where there is missing music and the standardized text is significantly shorter than the manuscript text

our current approach to handling missing music does not work. Put briefly, Cantus Ultimus tries to place the text around the missing music, but in this case there is no more text in the standardized version to go after the missing music.

This problem is not too difficult to solve, but does raise the question (in my mind) of whether we want to continue displaying the standardized text, or whether we want to follow in Cantus DB's footsteps and set the actual manuscript text to the volpiano melodies in search results. Thoughts on this last question, @annamorphism and @jacobdgm