python/retrace: Trim null chars.

They are often left in memory mapped files, and are not part of the XML
accept chars anyway.

src/gallium/state_trackers/python/retrace/parser.py

@@ -101,6 +101,7 @@ class XmlTokenizer:
             self.index = 0
             data = self.fp.read(size)
             self.final = len(data) < size
+            data = data.rstrip('\0')
             try:
                 self.parser.Parse(data, self.final)
             except xml.parsers.expat.ExpatError, e: