[ttLib] call XMLWriter.close() only if 'fileOrPath' is a path, not when it's a file

This allows to call `TTFont.saveXML` with an already open file/stream (e.g. sys.stdout or a StringIO) without it being abruptly closed at the end.

We do the same elsewhere when we reiceive file handles instead of path names, so we might do it here too.

Lib/fontTools/ttLib/__init__.py

@@ -308,7 +308,9 @@ class TTFont(object):
 			progress.set((i + 1))
 		writer.endtag("ttFont")
 		writer.newline()
-		writer.close()
+		# close if 'fileOrPath' is a path; leave it open if it's a file
+		if not hasattr(fileOrPath, "write"):
+			writer.close()
 
 	def _tableToXML(self, writer, tag, progress, quiet=None):
 		if quiet is not None: