Fix uninitialized variable in GoParser

[teemperor]

Summary

m_last_tok isn't initialized anywhere before it's used the first time (most likely in the GoParser::Rule::error method), which causes most of the GoParser tests to fail with sanitizers enabled with errors like this:

GoParser.cpp:52:21: runtime error: load of value <random value>, which is not a valid value for type 'GoLexer::TokenType'
UndefinedBehaviorSanitizer: undefined-behavior GoParser.cpp:52:21

[labath]

lgtm (the go plugin is kinda unmaintained now...)

[davide]

LGTM. FWIW, if people are not maintaining the Go and the Java plugin we should consider removing them entirely.
It's a huge amount of code and if there are no users/developers, it's really not worth the trouble.

source/Plugins/ExpressionParser/Go/GoParser.cpp

public:
   }
 
 private:
   llvm::StringRef m_name;
   GoParser *m_parser;
   size_t m_pos;
 };
 
-GoParser::GoParser(const char *src) : m_lexer(src), m_pos(0), m_failed(false) {}
+GoParser::GoParser(const char *src)
+    : m_lexer(src), m_pos(0), m_last_tok(GoLexer::TOK_INVALID),
+      m_failed(false) {}
 
 GoASTStmt *GoParser::Statement() {
   Rule r("Statement", this);
   GoLexer::TokenType t = peek();
   GoASTStmt *ret = nullptr;
   switch (t) {
   case GoLexer::TOK_EOF:
   case GoLexer::OP_SEMICOLON: