Utils: Bark when encountering a default-constructed QDir::Filter

This would always result in no hits, contrary to NoFilter.

Change-Id: I22591581373eed10fb1d1f660f705992e9653d5a
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/libs/utils/filepath.cpp

@@ -2173,6 +2173,7 @@ FileFilter::FileFilter(const QStringList &nameFilters,
       fileFilters(fileFilters),
       iteratorFlags(flags)
 {
+    QTC_CHECK(this->fileFilters != QDir::Filters());
 }
 
 QStringList FileFilter::asFindArguments(const QString &path) const