[LyX/2.1.x] Use isActive() instead of editable() in mathed.

[Jean-Marc Lasgouttes]

commit a6bc4a2a34a220f4ffd60743d3c5be9cbb9bf927
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Sun Mar 22 21:40:52 2015 +0100

    Use isActive() instead of editable() in mathed.
    
    Fixes crash introduced in [d5eeabcf/lyxgit].
    
    editable() is more related to Texted. It is false for closed collapsable 
insets
    Eventually the two methods should be merged.

diff --git a/src/DocIterator.cpp b/src/DocIterator.cpp
index e574115..db52912 100644
--- a/src/DocIterator.cpp
+++ b/src/DocIterator.cpp
@@ -555,8 +555,9 @@ void DocIterator::sanitize()
                        fixIfBroken();
                        break;
                }
-               if (!inset->editable()) {
-                       LYXERR0("Inset found on cursor stack is not editable.");
+               if ((inset->inMathed() && !inset->isActive())
+                   || (!inset->inMathed() && !inset->editable())) {
+                       LYXERR0("Inset found on cursor stack is not active.");
                        fixIfBroken();
                        break;
                }