Use isEmpty() instead of count() or size()

Change-Id: I0a89d2808c6d041da0dc41ea5aea58e6e8759bb4
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/git/branchmodel.cpp

@@ -179,7 +179,7 @@ public:
 
     QStringList childrenNames() const
     {
-        if (children.count() > 0) {
+        if (!children.isEmpty()) {
             QStringList names;
             for (BranchNode *n : children) {
                 names.append(n->childrenNames());