[LyX/master] Fix thinko in Buffer::preview. It is possible for this routine to be called when we do not have a cloned Buffer, namely, if we do not have EXPORT_in_THREAD defined.

[Richard Heck]

commit d8aab4af9e6e72c835f78ba54a46687b870c25fa
Author: Richard Heck <rgh...@lyx.org>
Date:   Sun Jul 10 01:12:42 2016 -0400

    Fix thinko in Buffer::preview. It is possible for this routine to
    be called when we do not have a cloned Buffer, namely, if we do not
    have EXPORT_in_THREAD defined.
---
 src/Buffer.cpp |   21 +++++++++------------
 1 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/src/Buffer.cpp b/src/Buffer.cpp
index a64e4b6..bcefe52 100644
--- a/src/Buffer.cpp
+++ b/src/Buffer.cpp
@@ -4315,10 +4315,10 @@ Buffer::ExportStatus Buffer::preview(string const & 
format, bool includeall) con
        ExportStatus const status = doExport(format, true, false, result_file);
        FileName const previewFile(result_file);
 
-       LATTEST (isClone());
-       d->cloned_buffer_->d->preview_file_ = previewFile;
-       d->cloned_buffer_->d->preview_format_ = format;
-       d->cloned_buffer_->d->preview_error_ = (status != ExportSuccess);
+       Impl * theimpl = isClone() ? d->cloned_buffer_->d : d;
+       theimpl->preview_file_ = previewFile;
+       theimpl->preview_format_ = format;
+       theimpl->preview_error_ = (status != ExportSuccess);
 
        if (status != ExportSuccess)
                return status;
@@ -4327,14 +4327,11 @@ Buffer::ExportStatus Buffer::preview(string const & 
format, bool includeall) con
                        return PreviewError;
                else
                        return PreviewSuccess;
-       }
-       else {
-               // Successful export but no output file?
-               // Probably a bug in error detection.
-               LATTEST (status != ExportSuccess);
-
-               return status;
-       }
+       } 
+       // Successful export but no output file?
+       // Probably a bug in error detection.
+       LATTEST(status != ExportSuccess);
+       return status;
 }