MimeDatabase: Avoid empty filter string in allFilterStrings.

Change-Id: I975423d2b0fcde7ff6e625e9d3cdaf271dd57dec
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/libs/utils/mimetypes/mimedatabase.cpp

@@ -323,8 +323,11 @@ QString MimeDatabase::allFiltersString(QString *allFilesFilter)
 {
     MimeDatabase mdb;
     QSet<QString> uniqueFilters;
-    foreach (const MimeType &mt, mdb.allMimeTypes())
-        uniqueFilters.insert(mt.filterString());
+    foreach (const MimeType &mt, mdb.allMimeTypes()) {
+        const QString &filterString = mt.filterString();
+        if (!filterString.isEmpty())
+            uniqueFilters.insert(mt.filterString());
+    }
     QStringList filters;
     foreach (const QString &filter, uniqueFilters)
         filters.append(filter);