ci: pr-check deal with scenario when no libs have changes

.github/workflows/pr-check.yml

@@ -25,7 +25,12 @@ jobs:
         id: libs
         run: |
           DIFF="$(git diff --name-only origin/${{ github.base_ref }} | xargs dirname | sort | uniq)"
-          LIBS=$(echo "${DIFF}" | grep '^platform/' | cut -d'/' -f2 | sort | uniq)
+          LIBDIFF="$(echo "${DIFF}" | grep '^platform/')"
+          if [ -z "${LIBDIFF}" ]; then
+            echo "list=[]" >> "$GITHUB_OUTPUT"
+            exit 0
+          fi
+          LIBS=$(echo "${LIBDIFF}" | cut -d'/' -f2 | sort | uniq)
           JSONARRAY=$(echo "${LIBS}" | jq -R -s -c 'split("\n")'[:-1])
           echo "list=${JSONARRAY}" >> "$GITHUB_OUTPUT"
         shell: bash