hopefully fix remove chord crash

gui.py

@@ -514,7 +514,8 @@ class DocumentWindow(QMainWindow):
                         if b.chord:
                             if b.chord.name == oldName:
                                 b.chord = None
-            self.window.blockTableView.populate(self.currentSection.blockList)
+            if self.currentSection.blockList is not None:
+                self.window.blockTableView.populate(self.currentSection.blockList)
             self.clearChordLineEdits()
             self.updateChordDict()