[Go] fix antlr.BaseLexer null pointer dereference

Fixes #3254; this is the exact fix recommended by @kaby76.

Author: SKalt

tool/resources/org/antlr/v4/tool/templates/codegen/Go/Go.stg

@@ -1423,7 +1423,7 @@ var lexerRuleNames []string
 <endif>
 
 type <lexer.name> struct {
-	*<if(superClass)><superClass><else>antlr.BaseLexer<endif>
+	<if(superClass)><superClass><else>*antlr.BaseLexer<endif>
 	channelNames []string
 	modeNames []string
 	// TODO: EOF string