fix "invalid read" errors from valgrind, prevent crash in XML parsing

[andresailer]

BEGINRELEASENOTES

• XMLParser: Fix "random" crash during XML parsing. Depends on XML Steering file and memory runtime behaviour, when some freed memory is overwritten

   /Marlin/source/tinyxml/src/tinyxml.cc:377: const TiXmlNode* TiXmlNode::IterateChildren(const char*, const TiXmlNode*) const: Assertion `previous->parent == this' failed.
  

• XMLParser: Fix "invalid read errors" reported by valgrind. Objects were removed before they were used again, which probably lead to the above mentioned crashs

ENDRELEASENOTES

crash

The crash can (maybe?) be reproduced with attached steering file (renamed to xml)
break.txt

source /cvmfs/clicdp.cern.ch/iLCSoft/builds/2019-02-20/x86_64-slc6-gcc62-opt/init_ilcsoft.sh
wget https://github.com/iLCSoft/Marlin/files/3013507/break.txt -O break.xml
Marlin break.xml

invalid read

Example valgrind output

==21315== Invalid read of size 8
==21315==    at 0x4ECA406: TiXmlNode::NextSibling(char const*) const (tinyxml.cc:386)
==21315==    by 0x4C8525B: IterateChildren (tinyxml.h:570)
==21315==    by 0x4C8525B: marlin::XMLParser::parse() (XMLParser.cc:160)
==21315==    by 0x40E5AE: main (Marlin.cc:277)
==21315==  Address 0x145894c0 is 96 bytes inside a block of size 216 free'd
==21315==    at 0x4A09186: operator delete(void*) (vg_replace_malloc.c:575)
==21315==    by 0x4ECA2F3: TiXmlNode::RemoveChild(TiXmlNode*) (tinyxml.cc:327)
==21315==    by 0x4C85417: marlin::XMLParser::parse() (XMLParser.cc:179)
==21315==    by 0x40E5AE: main (Marlin.cc:277)
==21315==  Block was alloc'd at
==21315==    at 0x4A080BC: operator new(unsigned long) (vg_replace_malloc.c:333)
==21315==    by 0x4ECF3A9: TiXmlNode::Identify(char const*, TiXmlEncoding) (tinyxmlparser.cc:892)
==21315==    by 0x4ED0C45: TiXmlElement::ReadValue(char const*, TiXmlParsingData*, TiXmlEncoding) (tinyxmlparser.cc:1229)
==21315==    by 0x4ED0FDE: TiXmlElement::Parse(char const*, TiXmlParsingData*, TiXmlEncoding) (tinyxmlparser.cc:1124)
==21315==    by 0x4ECF50C: TiXmlDocument::Parse(char const*, TiXmlParsingData*, TiXmlEncoding) (tinyxmlparser.cc:767)
==21315==    by 0x4ECAE0D: TiXmlDocument::LoadFile(_IO_FILE*, TiXmlEncoding) (tinyxml.cc:1077)
==21315==    by 0x4ECB0A6: TiXmlDocument::LoadFile(char const*, TiXmlEncoding) (tinyxml.cc:953)
==21315==    by 0x4C84002: LoadFile (tinyxml.h:1409)
==21315==    by 0x4C84002: marlin::XMLParser::parse() (XMLParser.cc:28)
==21315==    by 0x40E5AE: main (Marlin.cc:277)