Close editors and clear preview when opening a new book

src/calibre/gui2/tweak_book/boss.py

@@ -86,6 +86,9 @@ class Boss(QObject):
                   ' Convert your book to one of these formats first.') % _(' and ').join(sorted(SUPPORTED)),
                 show=True)
 
+        for name in editors:
+            self.close_editor(name)
+        self.gui.preview.clear()
         self.container_count = -1
         if self.tdir:
             shutil.rmtree(self.tdir, ignore_errors=True)

src/calibre/gui2/tweak_book/preview.py

@@ -235,10 +235,11 @@ class WebView(QWebView):
         settings.setAttribute(settings.DeveloperExtrasEnabled, True)
         settings.setDefaultTextEncoding('utf-8')
 
-        self.setHtml('<p>')
         self.page().setNetworkAccessManager(NetworkAccessManager(self))
         self.page().setLinkDelegationPolicy(self.page().DelegateAllLinks)
 
+        self.clear()
+
     def sizeHint(self):
         return self._size_hint
 
@@ -256,6 +257,9 @@ class WebView(QWebView):
             mf.setScrollBarValue(Qt.Vertical, val[1])
         return property(fget=fget, fset=fset)
 
+    def clear(self):
+        self.setHtml('<p>')
+
 class Preview(QWidget):
 
     def __init__(self, parent=None):
@@ -287,3 +291,6 @@ class Preview(QWidget):
             # Tell webkit to reload all html and associated resources
             self.view.refresh()
 
+    def clear(self):
+        self.view.clear()
+