build: fix signing of multiple rpm packages

scripts/build/sign_packages.sh

@@ -6,4 +6,7 @@ gpg --allow-secret-key-import --import ~/private-repo/signing/private.key
 
 cp ./scripts/build/rpmmacros ~/.rpmmacros
 
-./scripts/build/sign_expect $GPG_KEY_PASSWORD dist/*.rpm
+for package in dist/*.rpm; do
+    [ -e "$package" ] || continue
+    ./scripts/build/sign_expect $GPG_KEY_PASSWORD $package
+done