[source] build: avoid failing in append-metadata if image could not be generated

[LEDE Commits]

nbd pushed a commit to source.git, branch master:
https://git.lede-project.org/e23ff063d3d1ee6820daf170a2c4c0e1810e4591

commit e23ff063d3d1ee6820daf170a2c4c0e1810e4591
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Mon Dec 4 20:24:24 2017 +0100

    build: avoid failing in append-metadata if image could not be generated
    
    The image build might have failed due to a size check
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 include/image-commands.mk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/image-commands.mk b/include/image-commands.mk
index 1ec5252..8db046b 100644
--- a/include/image-commands.mk
+++ b/include/image-commands.mk
@@ -281,7 +281,7 @@ metadata_json = \
 	}'
 
 define Build/append-metadata
-	$(if $(SUPPORTED_DEVICES),echo $(call metadata_json,$(SUPPORTED_DEVICES)) | fwtool -I - $@)
+	$(if $(SUPPORTED_DEVICES),-echo $(call metadata_json,$(SUPPORTED_DEVICES)) | fwtool -I - $@)
 endef
 
 define Build/kernel2minor