fix(lazy): crash on iterating "delayedCalls" (#219)

* fix: crash on iterating "delayedCalls"

It looks like the code allowed "loadSentry()" to run more than once and
the first run would unset "delayedCalls" causing the second run to crash on
trying to iterate it.

* Null-check vm as it might not exist

lib/plugin.lazy.js

@@ -7,14 +7,16 @@ let SentryMock = {}
 <% } %>
 let sentryReadyResolve
 let loadInitiated = false
+let loadCompleted = false
 
 <% if (options.lazy.injectMock) { %>
-let loadCompleted = false
 const vueErrorHandler = VueLib.config.errorHandler
 
 VueLib.config.errorHandler = (error, vm, info) => {
   if (!loadCompleted) {
-    vm.$sentry.captureException(error)
+    if (vm) {
+      vm.$sentry.captureException(error)
+    }
 
     if (VueLib.util) {
       VueLib.util.warn(`Error in ${info}: "${error.toString()}"`, vm)
@@ -42,7 +44,7 @@ export default function SentryPlugin (ctx, inject) {
   ctx.$sentry = SentryMock
   <% } %>
 
-  const loadSentryHook = () => !loadInitiated && loadSentry(ctx, inject)
+  const loadSentryHook = () => attemptLoadSentry(ctx, inject)
 
   <% if (options.lazy.injectLoadHook) { %>
   inject('sentryLoad', loadSentryHook)
@@ -61,15 +63,31 @@ export default function SentryPlugin (ctx, inject) {
   ctx.$sentryReady = sentryReady
 }
 
-async function loadSentry (ctx, inject) {
+async function attemptLoadSentry(ctx, inject) {
+  if (loadInitiated) {
+    return
+  }
+
   loadInitiated = true
 
   if (!window.<%= globals.nuxt %>) {
     <% if (options.dev) { %>
     // eslint-disable-next-line no-console
     console.warn(`$sentryLoad was called but window.<%= globals.nuxt %> is not available, delaying sentry loading until onNuxtReady callback. Do you really need to use lazy loading for Sentry?`)
     <% } %>
+    <% if (options.lazy.injectLoadHook) { %>
     window.<%= globals.readyCallback %>(() => loadSentry(ctx, inject))
+    <% } else { %>
+    // Wait for onNuxtReady hook to trigger.
+    <% } %>
+    return
+  }
+
+  await loadSentry(ctx, inject)
+}
+
+async function loadSentry (ctx, inject) {
+  if (loadCompleted) {
     return
   }
 
@@ -107,8 +125,8 @@ async function loadSentry (ctx, inject) {
   Sentry.init(config)
   <% } %>
 
-  <% if (options.lazy.injectMock) { %>
   loadCompleted = true
+  <% if (options.lazy.injectMock) { %>
   window.removeEventListener('error', SentryMock.captureException)
 
   delayedCalls.forEach(([methodName, args]) => Sentry[methodName].apply(Sentry, args))