Avoid crash on app startup if the default font family is empty

Don't call first() on a potentially empty list of families. Fixes
a crash on startup on QNX for me.

Change-Id: I551d21dac8cfd104b774d6442bdbe1db35f8b75c
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 6 insertions, 3 deletions

diff --git a/src/gui/text/qfontdatabase.cpp b/src/gui/text/qfontdatabase.cpp
index e2898b078c..56930bfdc6 100644
--- a/src/gui/text/qfontdatabase.cpp
+++ b/src/gui/text/qfontdatabase.cpp
@@ -2535,9 +2535,12 @@ void QFontDatabasePrivate::load(const QFontPrivate *d, int script)
         family_list << req.families.at(0);
 
         // add the default family
-        QString defaultFamily = QGuiApplication::font().families().first();
-        if (! family_list.contains(defaultFamily))
-            family_list << defaultFamily;
+        auto families = QGuiApplication::font().families();
+        if (!families.isEmpty()) {
+            QString defaultFamily = families.first();
+            if (! family_list.contains(defaultFamily))
+                family_list << defaultFamily;
+        }
 
     }