Perl: protection against duplicate $r->sleep() calls.

Duplicate $r->sleep() and/or $r->has_request_body() calls result
in undefined behaviour (in practice, connection leaks were observed).
To prevent this, croak() added in appropriate places.

src/http/modules/perl/nginx.xs

diff --git a/src/http/modules/perl/nginx.xs b/src/http/modules/perl/nginx.xs
index 104def1..e9db2f7 100644
--- a/src/http/modules/perl/nginx.xs
+++ b/src/http/modules/perl/nginx.xs
@@ -400,6 +400,10 @@
 
     ngx_http_perl_set_request(r, ctx);
 
+    if (ctx->next) {
+        croak("has_request_body(): another handler active");
+    }
+
     if (r->headers_in.content_length_n <= 0 && !r->headers_in.chunked) {
         XSRETURN_UNDEF;
     }
@@ -1093,6 +1097,10 @@
 
     ngx_http_perl_set_request(r, ctx);
 
+    if (ctx->next) {
+        croak("sleep(): another handler active");
+    }
+
     sleep = (ngx_msec_t) SvIV(ST(1));
 
     ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,