Added pointer check in QFontDatabase::load

CID 11131 (#1 of 1): Dereference after null check (FORWARD_NULL)46.
var_deref_op: Dereferencing null pointer fe.

Change-Id: Ifc0cd0b208db511516db93c3d0e0367299df6d80
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@theqtcompany.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>

src/gui/text/qfontdatabase.cpp

@@ -2799,6 +2799,7 @@ void QFontDatabase::load(const QFontPrivate *d, int script)
         req.fallBackFamilies.clear();
     }
 
+    Q_ASSERT(fe);
     if (fe->symbol || (d->request.styleStrategy & QFont::NoFontMerging)) {
         for (int i = 0; i < QChar::ScriptCount; ++i) {
             if (!d->engineData->engines[i]) {