[LyX/master] Refresh file cache before checking existence

[Scott Kostyshak]

commit 43ca05ead4f7ea9b4fefe9888333fada4ae2d404
Author: Scott Kostyshak <skost...@lyx.org>
Date:   Tue Aug 18 21:55:59 2015 -0400

    Refresh file cache before checking existence
    
    This is done only inside LFUN_BUFFER_VIEW_CACHE so as to preserve
    the benefits of caching in other places.
    
    Without this commit, if a converter or a user (re)moves the preview
    file and then calls buffer-view-cache LyX will launch the viewer for
    a file that does not exist.
    
    For a discussion and use case, see:
    https://www.mail-archive.com/search?l=mid&q=55d393d7.6050...@lyx.org

diff --git a/src/Buffer.cpp b/src/Buffer.cpp
index 2a67292..09cff3c 100644
--- a/src/Buffer.cpp
+++ b/src/Buffer.cpp
@@ -2446,6 +2446,7 @@ bool Buffer::getStatus(FuncRequest const & cmd, 
FuncStatus & flag)
                break;
 
        case LFUN_BUFFER_VIEW_CACHE:
+               (d->preview_file_).refresh();
                enable = (d->preview_file_).exists();
                break;