Perl: NULL-terminate argument list.

perl_parse() function expects argv/argc-style argument list,
which according to the C standard must be NULL-terminated,
that is: argv[argc] == NULL.

This change fixes a crash (SIGSEGV) that could happen because
of the buffer overrun during perl module initialization.

Signed-off-by: Piotr Sikora <piotr@cloudflare.com>

src/http/modules/perl/ngx_http_perl_module.c

diff --git a/src/http/modules/perl/ngx_http_perl_module.c b/src/http/modules/perl/ngx_http_perl_module.c
index bf4d1fe..6a8894c 100644
--- a/src/http/modules/perl/ngx_http_perl_module.c
+++ b/src/http/modules/perl/ngx_http_perl_module.c
@@ -577,7 +577,7 @@
 
     n = (pmcf->modules != NGX_CONF_UNSET_PTR) ? pmcf->modules->nelts * 2 : 0;
 
-    embedding = ngx_palloc(cf->pool, (4 + n) * sizeof(char *));
+    embedding = ngx_palloc(cf->pool, (5 + n) * sizeof(char *));
     if (embedding == NULL) {
         goto fail;
     }
@@ -595,6 +595,7 @@
     embedding[n++] = "-Mnginx";
     embedding[n++] = "-e";
     embedding[n++] = "0";
+    embedding[n] = NULL;
 
     n = perl_parse(perl, ngx_http_perl_xs_init, n, embedding, NULL);