rpmbs: fix build on sisyphus

bin/rpmbs

@@ -251,9 +251,7 @@ if [ -n "$UPLOADNOW" ] && is_gear $SPECDIR ; then
 		echo "Prepare to publish to $GIRARHOST..."
 		cd $SPECDIR || fatal
 
-		# select needed branch
-		if [ -n "$BINARYREPO" ] ; then
-			set_usebranch
+		if set_usebranch ; then
 			checkout_usebranch || fatal
 		fi
 

share/eterbuild/functions/branch

@@ -11,6 +11,9 @@ set_usebranch()
 	#[ -f "$LISTNAMES" ] || fatal "Run with one spec inside gear repo"
 	USEBRANCH=$BINARYREPO
 
+	[ -n "$USEBRANCH" ] || return 1
+	[ "$USEBRANCH" = "sisyphus" ] && return 1
+
 	# TODO: drop support of it
 	# support for obsoleted M?? names
 	OLDBRANCH=$MDISTR
@@ -21,6 +24,8 @@ set_usebranch()
 			USEBRANCH=$OLDBRANCH
 		fi
 	fi
+
+	return 0
 }
 
 # used: USEBRANCH OLDBRANCH BPSPEC