fix empty download dir error

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@9462 3c298f89-4303-0410-b956-a3cf2f4a3e73

rules.mk

@@ -32,7 +32,7 @@ SUBDIR:=$(patsubst $(TOPDIR)/%,%,${CURDIR})
 
 OPTIMIZE_FOR_CPU:=$(ARCH)
 
-DL_DIR:=$(call qstrip,$(if $(CONFIG_DOWNLOAD_FOLDER), $(CONFIG_DOWNLOAD_FOLDER),$(TOPDIR)/dl))
+DL_DIR:=$(if $(call qstrip,$(CONFIG_DOWNLOAD_FOLDER)),$(call qstrip,$(CONFIG_DOWNLOAD_FOLDER)),$(TOPDIR)/dl)
 BIN_DIR:=$(TOPDIR)/bin
 INCLUDE_DIR:=$(TOPDIR)/include
 SCRIPT_DIR:=$(TOPDIR)/scripts