print message if crustify is not installed

contrib/uncrustify.sh

@@ -1,3 +1,14 @@
 #!/usr/bin/env bash
+
+set -eu
+
 DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
-find "$DIR/../src" \( -name "*.cpp" -o -name "*.c" -o -name "*.h" \) -exec uncrustify -c "$DIR/uncrustify.cfg" --replace --no-backup {} +
+
+if ! uncrustify --version >/dev/null; then
+  echo "you need to install uncrustify for indentation"
+  exit 1
+fi
+
+find "$DIR/../src" \( -name "*.cpp" -o -name "*.c" -o -name "*.h" \) \
+  -exec uncrustify -c "$DIR/uncrustify.cfg" --replace --no-backup {} + \
+  || true