Fix warnings about QFileInfo being called with empty path

(cherry picked from commit e98282fc)

src/plugins/projectexplorer/project.cpp

@@ -234,6 +234,8 @@ QString Project::projectDirectory() const
 
 QString Project::projectDirectory(const QString &proFile)
 {
+    if (proFile.isEmpty())
+        return QString();
     QFileInfo info(proFile);
     return info.absoluteDir().path();
 }

src/plugins/qt4projectmanager/wizards/targetsetuppage.cpp

@@ -353,7 +353,7 @@ TargetSetupPage::recursivelyCheckDirectoryForBuild(const QString &directory, con
 {
     QList<ImportInfo> results;
 
-    if (maxdepth <= 0)
+    if (maxdepth <= 0 || directory.isEmpty())
         return results;
 
     // Check for in-source builds first: