fix rustup-toolchain without arguments

diff --git a/rustup-toolchain b/rustup-toolchain
index 7e5d57349b9dd6298240c71ffbb11442abbce631..ca5508e225a11cf2a2b4d5fa1c90deb2e614f268 100755 (executable)
--- a/rustup-toolchain
+++ b/rustup-toolchain
@@ -30,7 +30,7 @@ else
     NEW_COMMIT="$1"
 fi
 echo "$NEW_COMMIT" > rust-version
-shift
+shift || true # don't fail if shifting fails
 
 # Check if we already are at that commit.
 CUR_COMMIT=$(rustc +miri --version -v 2>/dev/null | egrep "^commit-hash: " | cut -d " " -f 2)