Fix leak when unsetting PATH in main shell

src/cmd/ksh93/sh/path.c:
- Stop calling path_dup() on defpathinit() return value as it
  immediately raises the reference count of the path components to 2
  and makes it such that a single path_delete() is not sufficient for
  freeing the path components. The path_dup() call in path_addpath()
  which caused the leak was last strictly necessary probably in ksh93o.

Progresses: ksh93#405

src/cmd/ksh93/sh/path.c

@@ -393,8 +393,7 @@ static void pathinit(void)
 	}
 	else
 	{
-		pp = defpathinit();
-		sh.pathlist = (void*)path_dup(pp);
+		sh.pathlist = pp = (void*)defpathinit();
 	}
 	if(val=sh_scoped((FPATHNOD))->nvalue.cp)
 	{
@@ -1629,7 +1628,7 @@ Pathcomp_t *path_addpath(Pathcomp_t *first, register const char *path,int type)
 	if(old)
 	{
 		if(!first && !path)
-			first = path_dup(defpathinit());
+			first = (void*)defpathinit();
 		if(cp=(sh_scoped(FPATHNOD))->nvalue.cp)
 			first = (void*)path_addpath((Pathcomp_t*)first,cp,PATH_FPATH);
 		path_delete(old);

src/cmd/ksh93/tests/leaks.sh

@@ -360,7 +360,7 @@ DO
 	hash "${random_utils[@]}"
 DONE
 
-TEST	title='unset PATH in main shell' known=y url=https://github.com/ksh93/ksh/issues/405
+TEST	title='unset PATH in main shell'
 DO
 	unset PATH
 	PATH=$save_PATH