BUG/MEDIUM: stats: fix stats page regression introduced by commit 20b0de5

This commit adding http-request add-header/set-header unfortunately introduced
a regression to the handling of the stats page which is not matched anymore.

Thanks to Dmitry Sivachenko for reporting this.
diff --git a/src/proto_http.c b/src/proto_http.c
index c715828..deed52e 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -3113,11 +3113,11 @@
 				trash.str[trash.len++] = ' ';
 				trash.len += build_logline(s, trash.str + trash.len, trash.size - trash.len, &rule->arg.hdr_add.fmt);
 				http_header_add_tail2(&txn->req, &txn->hdr_idx, trash.str, trash.len);
-				break;
+				return rule;
 			}
 		}
 	}
-	return rule;
+	return NULL;
 }
 
 /* This stream analyser runs all HTTP request processing which is common to