mg: fix undo transpose-paragraph

[Mark Lumsden]

Currently undoing transpose-paragraph doesn't work as expected.
This diff fixes that.

ok?

Index: paragraph.c
===================================================================
RCS file: /cvs/src/usr.bin/mg/paragraph.c,v
retrieving revision 1.45
diff -u -p -r1.45 paragraph.c
--- paragraph.c 6 Sep 2016 16:25:47 -0000       1.45
+++ paragraph.c 13 Nov 2018 21:20:48 -0000
@@ -338,6 +338,8 @@ transposepara(int f, int n)
        if (n == 0)
                return (TRUE);

+       undo_boundary_enable(FFRAND, 0);
+
        /* find a paragraph, set mark, then goto the end */
        gotobop(FFRAND, 1);
        curwp->w_markp = curwp->w_dotp;
@@ -364,6 +366,8 @@ transposepara(int f, int n)
                return (FALSE);
        }
        (void)yank(FFRAND, 1);
+
+       undo_boundary_enable(FFRAND, 1);

        return (TRUE);
 }