reworked nvm check

Now the prompt segment just returns without doing anything if nvm is not present.

powerlevel9k.zsh-theme

@@ -531,14 +531,13 @@ prompt_node_version() {
 # Node version from NVM
 # Only prints the segment if different than the default value
 prompt_nvm() {
-  if [[ $(type nvm) =~ 'nvm is a shell function'* ]]; then
+  [[ $(type nvm) =~ 'nvm is a shell function'* ]] && return
   local node_version=$(nvm current)
   local nvm_default=$(cat $NVM_DIR/alias/default)
   [[ -z "${node_version}" ]] && return
   [[ "$node_version" =~ "$nvm_default" ]] && return
-  fi
 
-  [[ -n "${node_version}" ]] && $1_prompt_segment "$0" "$2" "green" "011" "${node_version:1}" 'NODE_ICON'
+  $1_prompt_segment "$0" "$2" "green" "011" "${node_version:1}" 'NODE_ICON'
 }
 
 # print a little OS icon