deal with onclick handlers that don't return false

Because <base> is set to the media server URL, <a href='#' ...> causes
a page transition from the current setHtml() page data. Previous Qt
versions allowed us to just ignore the request, but now returning False
in acceptNavigationRequest() causes the subsequent page navigation to
be rejected as well, resulting in no visible change when clicking on a
deck in the deck list.

To deal with this, Anki will now warn when such navigation requests
come in, as the anchors need to be updated to return false. pycmd()
has been updated to return false to make returning in onclick easier.

Also use QUrl.matches() instead of converting the potentially long
URL to a string.

aqt/deckbrowser.py

@@ -176,7 +176,7 @@ where id > ?""", (self.mw.col.sched.dayCutoff-86400)*1000)
         buf += """
 
         <td class=decktd colspan=5>%s%s<a class="deck %s"
-        href=# onclick="pycmd('open:%d')">%s</a></td>"""% (
+        href=# onclick="return pycmd('open:%d')">%s</a></td>"""% (
             indent(), collapse, extraclass, did, name)
         # due counts
         def nonzeroColour(cnt, colour):

aqt/webview.py

@@ -49,7 +49,8 @@ class AnkiWebPage(QWebEnginePage):
                         }
                     }
                 
-                    channel.objects.py.cmd(arg, resultCB);                   
+                    channel.objects.py.cmd(arg, resultCB);
+                    return false;                   
                 }
                 pycmd("domDone");
             });
@@ -71,9 +72,10 @@ class AnkiWebPage(QWebEnginePage):
         # data: links generated by setHtml()
         if url.scheme() == "data":
             return True
+        # catch buggy <a href='#' onclick='func()'> links
         from aqt import mw
-        # ignore href=#
-        if url.toString().startswith(mw.serverURL()):
+        if url.matches(QUrl(mw.serverURL()), QUrl.RemoveFragment):
+            sys.stderr.write("onclick handler needs to return false\n")
             return False
         # load all other links in browser
         openLink(url)