CppTools: Fix uninitialized memory

We cast it later to int64 for performance reasons so everything should be
filled by zeros.

Task-number: QTCREATORBUG-16672
Change-Id: Ib79ffa5cef79104dd3454111b52a6615c4b48917
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/cpptools/semantichighlighter.cpp

@@ -138,6 +138,7 @@ static TextStyles mixinStyle(TextStyle main, TextStyle mixin)
 {
     TextStyles res;
     res.mainStyle = main;
+    res.mixinStyles.fillWithZero();
     res.mixinStyles.push_back(mixin);
     return res;
 }