fix: avoid multiple verifyConditions invocation

closes semantic-release#414

index.js

@@ -14,6 +14,10 @@ let prepared;
 const npmrc = tempy.file({name: '.npmrc'});
 
 async function verifyConditions(pluginConfig, context) {
+  if (verified) {
+    return
+  }
+
   // If the npm publish plugin is used and has `npmPublish`, `tarballDir` or `pkgRoot` configured, validate them now in order to prevent any release if the configuration is wrong
   if (context.options.publish) {
     const publishPlugin =
@@ -39,7 +43,7 @@ async function verifyConditions(pluginConfig, context) {
     errors.push(...error);
   }
 
-  if (errors.length > 0) {
+  if (errors.length > 0 && verified === undefined) {
     throw new AggregateError(errors);
   }