Prevent crashes due to badly initialized of current Document

currentVivyDocument and currentScriptDocument macros don't always return
the "parent" document. This assumption lead to some badly initialized
data that considered the wrong document to be the "parent" of the view.

Fix the bad usage of those macros

src/Lib/Ass/Line.cc

@@ -7,6 +7,7 @@
 using namespace Vivy::Ass;
 
 Line::Line()
+    // FIXME SEVERE: use of currentVivyDocument?
     : assFactory(currentVivyDocument->getAssSubDocument()->getFactory())
 {
 }

src/UI/DocumentViews/AudioVisualizer/TimingScene.cc

@@ -81,18 +81,25 @@ TimingScene::rebuildScene()
     addItem(cursor);
     cursor->setPos(0, TimingUtils::axisHeight());
 
-    if (auto assDocument = currentVivyDocument->getAssSubDocument()) {
-        QVector<Ass::LinePtr> lines = assDocument->getLines();
-        for (int i = 0; i < lines.size(); ++i) {
-            if (auto line = lines.at(i).get()) {
-                TimingLine *l = new TimingLine(line, i);
-                l->setVisible(false);
-                addItem(l);
-                timingLines.append(l);
-                if (auto p = rootView.lock()) {
-                    if (auto assLinesModel = p->getAssLinesModel()) {
-                        connect(l, &TimingLine::lineChanged, assLinesModel,
-                                &AssLinesModel::updateLine);
+    // FIXME: bruh
+    if (auto p = rootView.lock()) {
+        if (auto v = p.get()) {
+            if (auto d = v->getDocument()) {
+                if (auto assDocument = d->getAssSubDocument()) {
+                    QVector<Ass::LinePtr> lines = assDocument->getLines();
+                    for (int i = 0; i < lines.size(); ++i) {
+                        if (auto line = lines.at(i).get()) {
+                            TimingLine *l = new TimingLine(line, i);
+                            l->setVisible(false);
+                            addItem(l);
+                            timingLines.append(l);
+                            if (auto p = rootView.lock()) {
+                                if (auto assLinesModel = p->getAssLinesModel()) {
+                                    connect(l, &TimingLine::lineChanged, assLinesModel,
+                                            &AssLinesModel::updateLine);
+                                }
+                            }
+                        }
                     }
                 }
             }

src/VivyApplication.hh

@@ -16,6 +16,12 @@
 #define VIVY_APP_LOGGABLE_OBJECT_BY_STORED_NAME(name, logger) \
     VIVY_LOGGABLE_OBJECT_BY_STORED_NAME(vivyApp->getLogSink(), name, logger)
 
+/*
+ * Be careful when using those two macros
+ * What you get here is the document currently selected as the current tab
+ * Fore exemple, there is no guarantee that this is the same document that
+ * the parent of a subDocument View you're calling those macros from
+ */
 #define currentVivyDocument   dynamic_cast<VivyDocument *>(vivyApp->getCurrentDocument())
 #define currentScriptDocument dynamic_cast<ScriptDocument *>(vivyApp->getCurrentDocument())