ZIP Output: Fix system encoding being used instead of UTF-8 for html files. See #1499514 (Latin encode error while converting from epub to htmlz)

src/calibre/ebooks/conversion/plugins/html_output.py

@@ -127,6 +127,8 @@ class HTMLOutput(OutputFormatPlugin):
                     toc=html_toc, meta=meta, nextLink=nextLink,
                     tocUrl=tocUrl, cssLink=cssLink,
                     firstContentPageLink=nextLink)
+            if isinstance(t, unicode):
+                t = t.encode('utf-8')
             f.write(t)
 
         with CurrentDir(output_dir):

src/templite/__init__.py

@@ -84,4 +84,4 @@ class Templite(object):
 
     def write(self, *args):
         for a in args:
-            self.__output.append(str(a))
+            self.__output.append(unicode(a))