QMap: don't dereference nullptr

root(), leftNode() and rightNode() can be nullptr.
These pieces of code happened to work because the first thing lowerBound()
does is

   Node *n = this;
   // ...
   while (n)
     // ...

But that is _after_ dereferencing nullptr, which is undefined behavior.

So, check first, then deref.

Change-Id: I9137bf6e21014cd68404a7e49a748910b1d768cf
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/src/corelib/tools/qmap.h b/src/corelib/tools/qmap.h
index 29e8f9b140..0e32ade94d 100644
--- a/src/corelib/tools/qmap.h
+++ b/src/corelib/tools/qmap.h
@@ -288,9 +288,11 @@ void QMapData<Key, T>::deleteNode(QMapNode<Key, T> *z)
 template <class Key, class T>
 QMapNode<Key, T> *QMapData<Key, T>::findNode(const Key &akey) const
 {
-    Node *lb = root()->lowerBound(akey);
-    if (lb && !qMapLessThanKey(akey, lb->key))
-        return lb;
+    if (Node *r = root()) {
+        Node *lb = r->lowerBound(akey);
+        if (lb && !qMapLessThanKey(akey, lb->key))
+            return lb;
+    }
     return 0;
 }
 
@@ -307,10 +309,10 @@ void QMapData<Key, T>::nodeRange(const Key &akey, QMapNode<Key, T> **firstNode,
         } else if (qMapLessThanKey(n->key, akey)) {
             n = n->rightNode();
         } else {
-            *firstNode = n->leftNode()->lowerBound(akey);
+            *firstNode = n->leftNode() ? n->leftNode()->lowerBound(akey) : 0;
             if (!*firstNode)
                 *firstNode = n;
-            *lastNode = n->rightNode()->upperBound(akey);
+            *lastNode = n->rightNode() ? n->rightNode()->upperBound(akey) : 0;
             if (!*lastNode)
                 *lastNode = l;
             return;