Fix downloads with unknown size with WebEngine

qutebrowser/browser/downloads.py

@@ -240,7 +240,7 @@ class DownloadItemStats(QObject):
             bytes_done: How many bytes are downloaded.
             bytes_total: How many bytes there are to download in total.
         """
-        if bytes_total == -1:
+        if bytes_total in [0, -1]:  # QtWebEngine, QtWebKit
             bytes_total = None
         self.done = bytes_done
         self.total = bytes_total
@@ -311,10 +311,12 @@ class AbstractDownloadItem(QObject):
             errmsg = ""
         else:
             errmsg = " - {}".format(self.error_msg)
+
         if all(e is None for e in [perc, remaining, self.stats.total]):
             return ('{index}: {name} [{speed:>10}|{down}]{errmsg}'.format(
                 index=self.index, name=self.basename, speed=speed,
                 down=down, errmsg=errmsg))
+
         perc = round(perc)
         if remaining is None:
             remaining = '?'

tests/end2end/features/downloads.feature

@@ -503,3 +503,9 @@ Feature: Downloading things from a website.
         And I wait until the download is finished
         Then the downloaded file download.bin should exist
         And the downloaded file download2.bin should not exist
+
+    Scenario: Downloading a file with unknown size
+       When I set storage -> prompt-download-directory to false
+       And I open stream-bytes/1024 without waiting
+       And I wait until the download is finished
+       Then the downloaded file 1024 should exist