mkdir -p "$STACKED_REBASE_DIR" in post-rewrite script

Signed-off-by: Kipras Melnikovas <kipras@kipras.org>

Author: kiprasmel

git-stacked-rebase.ts

@@ -632,6 +632,8 @@ REWRITTEN_LIST_FILE_PATH="$REBASE_MERGE_DIR/${filenames.rewrittenList}"
 STACKED_REBASE_DIR="$(pwd)/.git/stacked-rebase"
 REWRITTEN_LIST_BACKUP_FILE_PATH="$STACKED_REBASE_DIR/${filenames.rewrittenList}"
 
+mkdir -p "$STACKED_REBASE_DIR"
+
 #echo "REBASE_MERGE_DIR $REBASE_MERGE_DIR; STACKED_REBASE_DIR $STACKED_REBASE_DIR;"
 
 #cp "$REWRITTEN_LIST_FILE_PATH" "$REWRITTEN_LIST_BACKUP_FILE_PATH"