ProjectManager: Fix Project::findNodeForBuildKey()

Amends c58da42bab.

This operates also on not-fully loaded projects now, which was
previously causing a crash on android projects.

Change-Id: I44eeb7af8ed53a47ef39e7f1bafb07b871879ce5
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/projectexplorer/project.cpp

@@ -886,9 +886,11 @@ bool Project::hasParsingData() const
 const ProjectNode *Project::findNodeForBuildKey(const QString &buildKey) const
 {
     const ProjectNode *result = nullptr;
+    if (d->m_rootProjectNode) {
         d->m_rootProjectNode->forEachProjectNode([buildKey](const ProjectNode *node) {
             return node->buildKey() == buildKey;
         });
+    }
     return result;
 }