[patch] fix crash on command line with branches

[Jürgen Spitzmüller]

http://bugzilla.lyx.org/show_bug.cgi?id=4255

The patch looks straightforward to me. Abdel, what do you think?

Jürgen

Index: src/BranchList.cpp
===================================================================
--- src/BranchList.cpp	(Revision 20838)
+++ src/BranchList.cpp	(Arbeitskopie)
@@ -24,7 +24,9 @@
 
 Branch::Branch() : selected_(false)
 {
-	theApp()->getRgbColor(Color::background, color_);
+	// no theApp() with command line export
+	if (theApp())
+		theApp()->getRgbColor(Color::background, color_);
 }