fix problems with dll

lib/builder/builder.js

@@ -81,7 +81,12 @@ export default class Builder extends Tapable {
     const vendor = this.vendor()
     const vendorEntries = {}
     vendor.forEach(v => {
-      vendorEntries[v] = [ v ]
+      try {
+        require.resolve(v)
+        vendorEntries[v] = [ v ]
+      } catch (e) {
+        // Ignore
+      }
     })
     return vendorEntries
   }

lib/builder/webpack/client.config.js

@@ -174,7 +174,9 @@ export default function webpackClientConfig () {
           )
         }
       })
-      debug('[DLL] ' + _dlls.join(','))
+      if (_dlls.length) {
+        debug('Using dll for ' + _dlls.join(','))
+      }
     }
   }