QmlJS: Fix crash in PathsAndLanguages::compact()

Task-number: QTCREATORBUG-13786
Change-Id: If8c84714382c751f51315d62e1d4b0764e4431ff
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@theqtcompany.com>

src/libs/qmljs/qmljsdialect.cpp

@@ -300,7 +300,11 @@ bool PathsAndLanguages::maybeInsert(const PathAndLanguage &pathAndLanguage) {
     return true;
 }
 
-void PathsAndLanguages::compact() {
+void PathsAndLanguages::compact()
+{
+    if (m_list.isEmpty())
+        return;
+
     int oldCompactionPlace = 0;
     Utils::FileName oldPath = m_list.first().path();
     QList<PathAndLanguage> compactedList;