Fix right_boundary properly after a row is shortened

Instead of resetting it to false, do a proper test to see whether
there is a separator at the end of the row.

Fixes bug #10180.
(cherry picked from commit 5e5440f2f3)

src/TextMetrics.cpp

@@ -917,7 +917,7 @@ void TextMetrics::breakRow(Row & row, int const right_margin, pit_type const pit
 	// if the row is too large, try to cut at last separator. In case
 	// of success, reset indication that the row was broken abruptly.
 	if (row.shortenIfNeeded(body_pos, width))
-		row.right_boundary(false);
+		row.right_boundary(!row.empty() && row.back().endpos == row.endpos());
 
 	// make sure that the RTL elements are in reverse ordering
 	row.reverseRTL(is_rtl);

status.22x

@@ -98,9 +98,6 @@ What's new
 
 - Fix on screen narrow box when using \width as box width unit (bug 10048).
 
-- Fix horizontal scrolling feature when inside a collapsable inset
-  with several paragraphs.
-
 - Raise GuiView on buffer switch to bring it topmost in multi-window mode.
 
 - Fix smal typo in Reference dialog (bug 10194).
@@ -123,6 +120,9 @@ What's new
 - Fix selection of large formula with the mouse when horizontal
   scrolling kicks in (but 10094).
 
+- Fix bug where cursor can't be put at the end of a line before an
+  inset (bug 10180).
+
 - Fix display of collapsable insets when the same document is shown in
   two views with different width (bug 9756).