Make sure we have binaries before trying to format them

Otherwise basename spits out errors #8

zsh-nvm.plugin.zsh

@@ -23,10 +23,17 @@ _zsh_nvm_install() {
 }
 
 _zsh_nvm_global_binaries() {
+
+  # Look for global binaries
+  local global_binary_paths=$(echo "$NVM_DIR"/v0*/bin/*(N) "$NVM_DIR"/versions/*/*/bin/*(N))
+
+  # If we have some, format them
+  if [[ -n "$global_binary_paths" ]]; then
     echo "$NVM_DIR"/v0*/bin/*(N) "$NVM_DIR"/versions/*/*/bin/*(N) |
       xargs -n 1 basename |
       sort |
       uniq
+  fi
 }
 
 _zsh_nvm_load() {