plot.py: prevent early removal of file

savefig might call close on the temporary file, hence the picture is
removed before the viewer can open it.

Credits francois

Author: teto

mptcpanalyzer/plot.py

@@ -307,7 +307,7 @@ def postprocess(self, v, display: bool=False, out=None, **opt):
 
         if display:
             if out is None:
-                with tempfile.NamedTemporaryFile() as tmpfile:
+                with tempfile.NamedTemporaryFile(delete=False) as tmpfile:
                     print("No output file set, using tempfile=%s" % tmpfile)
                     r = self.savefig(v, tmpfile.name)
                     log.debug("returned %r" % r)