base-files: sysupgrade: exit if the firmware download failed

Sysupgrade process shouldn't continue if the firmware image couldn't be
downloaded.

Ref: http://lists.infradead.org/pipermail/openwrt-devel/2019-December/020940.html
Reported-by: Petr Novák <petrn@me.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>
(cherry picked from commit cf3da66d2ce11a30ae2993b56276ade10c9bddb9)

package/base-files/Makefile

@@ -12,7 +12,7 @@ include $(INCLUDE_DIR)/version.mk
 include $(INCLUDE_DIR)/feeds.mk
 
 PKG_NAME:=base-files
-PKG_RELEASE:=204.1
+PKG_RELEASE:=204.2
 PKG_FLAGS:=nonshared
 
 PKG_FILE_DEPENDS:=$(PLATFORM_DIR)/ $(GENERIC_PLATFORM_DIR)/base-files/

package/base-files/files/sbin/sysupgrade

@@ -294,7 +294,7 @@ type platform_check_image >/dev/null 2>/dev/null || {
 case "$IMAGE" in
 	http://*|\
 	https://*)
-		wget -O/tmp/sysupgrade.img "$IMAGE"
+		wget -O/tmp/sysupgrade.img "$IMAGE" || exit 1
 		IMAGE=/tmp/sysupgrade.img
 		;;
 esac