git-cp: don't stop execution when merge.ff is not set (#1096)

Signed-off-by: spacewander <spacewanderlzx@gmail.com>

Author: spacewander

bin/git-cp

@@ -51,7 +51,7 @@ else
     fi
 
     MERGE_OPT=
-    ff=$(git config --get merge.ff)
+    ff=$(git config --get merge.ff || true)
     if [[ "$ff" == "only" ]]; then
         MERGE_OPT="--ff"
     fi