Reinstate mungeHTML in editor.py

The removal of this function in #270 causes <br> to remain in seemingly
empty editor fields, which in turn wrongly prompts the "Close and lose
current input?" dialog.

aqt/editor.py

@@ -254,6 +254,7 @@ class Editor:
                 return
             txt = urllib.parse.unquote(txt)
             txt = unicodedata.normalize("NFC", txt)
+            txt = self.mungeHTML(txt)
             # misbehaving apps may include a null byte in the text
             txt = txt.replace("\x00", "")
             # reverse the url quoting we added to get images to display
@@ -285,6 +286,10 @@ class Editor:
         else:
             print("uncaught cmd", cmd)
 
+    def mungeHTML(self, txt):
+        txt = re.sub(r"<br>$", "", txt)
+        return txt
+
     # Setting/unsetting the current note
     ######################################################################