report fails to read xml produced by record due to extraneous empty elements

[derekbruening]

There are extraneous empty elements in the xml produced:

$ ./roofline.py record ~/dr/test/roofline 1 100000
/mypath/extsw/roofline//dynamorio/build/bin64/drrun  -c /mypath/extsw/roofline//client/build/libroofline.so --output_folder /mypath/extsw/roofline//mypath/dr/test/roofline_1_1000002021-05-11_02:24:21/       -- /mypath/dr/test/roofline 1 100000
> Roofline is running to get FP and Bytes accessed.
<wrapping _RoiStart @0x00007ff57b900275
<wrapping _RoiEnd @0x00007ff57b900287
Estimation of pi is 3.141592653598162
Received 29 alarms
/mypath/extsw/roofline//dynamorio/build/bin64/drrun  -c /mypath/extsw/roofline//client/build/libroofline.so --output_folder /mypath/extsw/roofline//mypath/dr/test/roofline_1_1000002021-05-11_02:24:21/       --time_run -- /mypath/dr/test/roofline 1 100000
> Roofline is running for gathering timining information
<wrapping _RoiStart @0x00007f0eafb67275
<wrapping _RoiEnd @0x00007f0eafb67287
Estimation of pi is 3.141592653598162
Received 2 alarms

$ ./roofline.py report -i mypath/dr/test/roofline_1_1000002021-05-11_02\:24\:21 --line myhost_FP64 --output_dir out
Roofline: building report merging a roofline for myhost_FP64 precision. Please make sure you target application has used the same precision
Traceback (most recent call last):
  File "/mypath/extsw/roofline/./roofline.py", line 694, in <module>
    sys.exit(main())
  File "/mypath/extsw/roofline/./roofline.py", line 690, in main
    args.func(args)
  File "/mypath/extsw/roofline/./roofline.py", line 452, in report
    current_points = get_points(in_dir, colour_n+1, get_app_title(in_dir))
  File "/mypath/extsw/roofline/./roofline.py", line 131, in get_points
    root = ET.parse(in_dir + '/roofline.xml').getroot()
  File "/usr/lib/python3.9/xml/etree/ElementTree.py", line 1229, in parse
    tree.parse(source, parser)
  File "/usr/lib/python3.9/xml/etree/ElementTree.py", line 580, in parse
    self._root = parser._parse_whole(source)
xml.etree.ElementTree.ParseError: junk after document element: line 14, column 0

Here's the roofline.xml file:

<?xml version="1.0"?>
<roofline>
<point label="pi_estimation">
<flops>700004</flops>
<bytes>124807562</bytes>
<read_bytes>59204690</read_bytes>
<write_bytes>65602872</write_bytes>
<src_file_start>/mypath/dr/test/roofline.cpp</src_file_start>
<src_file_end>/mypath/dr/test/roofline.cpp</src_file_end>
<line_n_start>69</line_n_start>
<line_n_end>91</line_n_end>
</point>
</roofline>
<?xml version="1.0"?>
<roofline>
</roofline>

Note the final 3 lines: when I remove them (and similar lines in roofline_time.xml) then the report successfully parses them.