[MusicXML import] incorrect font size in title frame when credit-words size unspecified

When credit-words do not contain an explicit font size or when no credit-words are present (and meta data is used to build the title frame), the font size is taken from the word-font element. This typically results in all texts in the title frame being very small. Minor issue, as this can be fixed easily by using Format / Reset Style.

Solution is trivial. This is a regression introduced in 3.5.