QmlJS: Fix plugin dumpers running all the time if dump fails.

Task-number: QTCREATORBUG-2733
Reviewed-by: Kai Koehne

src/libs/qmljs/qmljsdocument.cpp

@@ -358,6 +358,7 @@ LibraryInfo::LibraryInfo(const QmlDirParser &parser)
     : _valid(true)
     , _components(parser.components())
     , _plugins(parser.plugins())
+    , _dumped(false)
 {
 }