scripts/mkimage: show message when temp folder is full

If temporary folder is full error message can't be saved and shown to the user which doesn't know what the problem actually is. In this case file is empty and show other message.

scripts/mkimage

@@ -39,11 +39,16 @@ cleanup() {
 }
 
 show_error() {
-  echo -e "image: error happen...\n"
-  cat "${SAVE_ERROR}"
+  echo "image: An error has occurred..."
   echo
+  if [ -s "${SAVE_ERROR}" ]; then
+    cat "${SAVE_ERROR}"
+  else
+    echo "Folder $LE_TMP might be out of free space..."
+  fi
+  echo 
   cleanup
-  exit 1
+  die
 }
 
 trap cleanup SIGINT