Do not try to extract text from DRM-ed files

svn path=/trunk/playground/graphics/okular/mobipocket/; revision=903974

mobiendanalyzer.cpp

@@ -91,8 +91,10 @@ MobiEndAnalyzer::analyze(AnalysisResult& as, InputStream* in) {
             case Mobipocket::Document::Copyright: as.addValue(factory->copyrightField, it.value().toUtf8().data() ); break;
         }
     }
-    QByteArray text=doc.text(20480).toUtf8();
-    as.addText(text.data(), text.size());
+    if (!doc.hasDRM()) {
+        QByteArray text=doc.text(20480).toUtf8();
+        as.addText(text.data(), text.size());
+    }
     return 0;
 }