[LyX/master] Do not write an empty default_otf_view_format.

[Juergen Spitzmueller]

commit 79a59fce1d5d1bdc5b46ba430cc8a5be956f19d9
Author: Juergen Spitzmueller <sp...@lyx.org>
Date:   Mon Apr 28 14:59:03 2014 +0200

    Do not write an empty default_otf_view_format.
    
    Fixes: #9100.

diff --git a/src/LyXRC.cpp b/src/LyXRC.cpp
index 80b8514..c95cacd 100644
--- a/src/LyXRC.cpp
+++ b/src/LyXRC.cpp
@@ -2829,8 +2829,9 @@ void LyXRC::write(ostream & os, bool ignore_system_lyxrc, 
string const & name) c
                        break;
        }
        case RC_DEFAULT_OTF_VIEW_FORMAT:
-               if (ignore_system_lyxrc ||
-                   default_otf_view_format != 
system_lyxrc.default_otf_view_format) {
+        if ((ignore_system_lyxrc ||
+            default_otf_view_format != system_lyxrc.default_otf_view_format)
+            && !default_otf_view_format.empty()) {
                        os << "\\default_otf_view_format " << 
default_otf_view_format << '\n';
                }
                if (tag != RC_LAST)