Qbs: Avoid double call to a virtual function

Change-Id: If0bae8b2c8cce6542cbd6fd8df867fc200feb37d
Reviewed-by: Jake Petroules <jake.petroules@theqtcompany.com>

src/plugins/qbsprojectmanager/qbsrunconfiguration.cpp

@@ -255,7 +255,7 @@ QString QbsRunConfiguration::baseWorkingDirectory() const
 {
     const QString exe = executable();
     if (!exe.isEmpty())
-        return QFileInfo(executable()).absolutePath();
+        return QFileInfo(exe).absolutePath();
     return QString();
 }