[zsh] temporarily fix zplg errors caused by detached HEAD in plugins

upgrade.zsh

@@ -4,6 +4,8 @@ DOTFILES_PATH="${0:a:h}"
 cd "$DOTFILES_PATH" || exit 1
 ZSH_DOTFILES="$DOTFILES_PATH/zsh"
 
+source "$ZSH_DOTFILES/functions.zsh"
+
 git pull --rebase --stat origin master
 git submodule update --init --recursive --remote --progress
 

zsh/zplg.zsh

@@ -151,7 +151,7 @@ _zplg_load() {
 
   _zplg_source_git_upgrade() {
     local plugin_url="$1" plugin_dir="$2"
-    ( cd "$plugin_dir" && git pull && git submodule update --init --recursive )
+    ( cd "$plugin_dir" && (git pull || git fetch) && git submodule update --init --recursive )
   }
 
   # small helper for the git source