Merge branch 'fix/cached-npm-completion'

Fixes #5332

plugins/npm/npm.plugin.zsh

@@ -2,10 +2,13 @@
     __NPM_COMPLETION_FILE="${ZSH_CACHE_DIR}/npm_completion"
 
     if [[ ! -f $__NPM_COMPLETION_FILE ]]; then
-        npm completion >! $__NPM_COMPLETION_FILE || rm -f $__NPM_COMPLETION_FILE
+        npm completion >! $__NPM_COMPLETION_FILE 2>/dev/null
+        [[ $? -ne 0 ]] && rm -f $__NPM_COMPLETION_FILE
     fi
 
-    source $__NPM_COMPLETION_FILE
+    [[ -f $__NPM_COMPLETION_FILE ]] && source $__NPM_COMPLETION_FILE
+
+    unset __NPM_COMPLETION_FILE
 }
 
 # Install dependencies globally