Returns the starting position of a given paragraph. Paragraphs are numbered starting with 0.
Calling this method may force the recalculation of location information if a maximum width is set for the editor, even if the editor currently has delayed refreshing (see refresh-delayed?). If the editor is not displayed and the editor has a maximum width, line breaks are calculated as for line-start-position.
If there are fewer than paragraph-1 paragraphs, the start of the last paragraph is returned.
If the paragraph starts with invisible items and visible? is not #f, the first position past the invisible items is returned.