Don't insert an extra space at the end of the line when doing a soft fold.

Trailing whitespaces are best avoided.

dkim/__init__.py

@@ -371,7 +371,7 @@ def fold(header, namelen=0):
     >>> text(fold(b'foo'))
     'foo'
     >>> text(fold(b'foo  '+b'foo'*24).splitlines()[0])
-    'foo  '
+    'foo '
     >>> text(fold(b'foo'*25).splitlines()[-1])
     ' foo'
     >>> len(fold(b'foo'*25).splitlines()[0])
@@ -399,9 +399,10 @@ def fold(header, namelen=0):
         i = header[:maxleng].rfind(b" ")
         if i == -1:
             j = maxleng
+            pre += header[:j] + b"\r\n "
         else:
             j = i + 1
-        pre += header[:j] + b"\r\n "
+            pre += header[:i] + b"\r\n "
         header = header[j:]
         maxleng = 72
     if len(header) > 2: