WIPE_PATCH isnt defined so dont generate a garbage rule

package/wipe/wipe.mk

@@ -15,8 +15,10 @@ WIPE_TARGET_BINARY:=bin/wipe
 $(DL_DIR)/$(WIPE_SOURCE):
 	 $(WGET) -P $(DL_DIR) $(WIPE_SITE)/$(WIPE_SOURCE)
 
+ifneq ($(WIPE_PATCH),)
 $(DL_DIR)/$(WIPE_PATCH):
 	 $(WGET) -P $(DL_DIR) $(WIPE_SITE)/$(WIPE_PATCH)
+endif
 
 wipe-source: $(DL_DIR)/$(WIPE_SOURCE) $(DL_DIR)/$(WIPE_PATCH)