[LyX/2.1.x] Fix reversion of box insets. (cherry picked from commit da75d3194824c87e2b2fc92fa4644e080aeaf962)

[Richard Heck]

commit 94ed54b51a676fe395809493a7a38dec0cc2b44c
Author: Enrico Forestieri <for...@lyx.org>
Date:   Thu May 29 10:44:02 2014 +0200

    Fix reversion of box insets.
    (cherry picked from commit da75d3194824c87e2b2fc92fa4644e080aeaf962)

diff --git a/lib/lyx2lyx/lyx_2_1.py b/lib/lyx2lyx/lyx_2_1.py
index 4dab15b..27f7faa 100644
--- a/lib/lyx2lyx/lyx_2_1.py
+++ b/lib/lyx2lyx/lyx_2_1.py
@@ -4197,7 +4197,7 @@ def revert_mbox_fbox(document):
             i += 1
             continue
         BeginLayout = find_token(document.body, "\\begin_layout Plain Layout", 
j)
-        EndLayout = find_token(document.body, "\\end_layout", BeginLayout)
+        EndLayout = find_end_of_layout(document.body, BeginLayout)
         # replace if width is ""
         if (width == '""'):
             document.body[EndLayout:k + 1] = put_cmd_in_ert("}")