If PASSWORD_STORE_SIGNING_KEY is not set, don't chmod the missing file

[f1shbot]

I was getting errors when running pass close regarding a chmod error. This was because I didn't have PASSWORD_STORE_SIGNING_KEY set. Here is a quick patch to fix the issue:

index 17c8ff3..1c910a1 100755
--- a/coffin.bash
+++ b/usr/lib/password-store/extensions/coffin.bash
@@ -77,8 +77,10 @@ coffin_close() {

   chmod 400 "$coffin_file" \
     || coffin_warn "unable to make the coffin a readonly file"
-  chmod 400 "$coffin_file.sig" \
-    || coffin_warn "unable to make the coffin signature a readonly file"
+  if [[ -n $PASSWORD_STORE_SIGNING_KEY ]]; then
+    chmod 400 "$coffin_file.sig" \
+      || coffin_warn "unable to make the coffin signature a readonly file"
+  fi

   # delete the remaining data inside PREFIX (PASSWORD_STORE_DIR)
   # CAVEAT: pass init supports specifying different .gpg-id files for different

[ayushnix]

Thanks @shawndfisher! I've merged your patch.