Preserve trailing spaces with capture-pane -J, from George Nachman.

cmd-capture-pane.c

@@ -111,7 +111,7 @@ cmd_capture_pane_exec(struct cmd *self, struct cmd_q *cmdq)
 		gc = NULL;
 		for (i = top; i <= bottom; i++) {
 			line = grid_string_cells(gd, 0, i, sx, &gc, with_codes,
-			    escape_c0);
+			    escape_c0, !join_lines);
 			linelen = strlen(line);
 
 			buf = xrealloc(buf, 1, len + linelen + 1);