TextBoxWidget: fix infinite loop when very small width

frontend/ui/widget/textboxwidget.lua

@@ -310,6 +310,15 @@ function TextBoxWidget:_splitToLines()
             --   which is a bit strange but that's what the use_xtext=false does.
             -- - Between a line end_offset= and the next line offset=, there may be only
             --   a single indice not included: the \n or the space that allowed the break.
+            --
+            if line.next_start_offset and line.next_start_offset == line.offset then
+                -- No char could fit (too small targeted_width)
+                -- makeLine 6509 { ["offset"] = 1, ["end_offset"] = 0, ["next_start_offset"] = 1,
+                -- ["width"] = 0, ["targeted_width"] = 7, ["no_allowed_break_met"] = true, ["can_be_justified"] = true
+                -- Make one char on this line
+                line.next_start_offset = line.offset + 1
+                line.width = targeted_width
+            end
             self.vertical_string_list[ln] = line
             if line.no_allowed_break_met then
                 -- let the fact a long word was splitted be known