do not fail on set empty servers list, covered with test

pinba.c

@@ -2481,7 +2481,7 @@ static PHP_INI_MH(OnUpdateCollectorAddress) /* {{{ */
 
 	php_pinba_cleanup_collectors(PINBA_G(collectors), &PINBA_G(n_collectors));
 
-	for (tmp = copy; (address = strsep(&tmp, ", ")); /**/) {
+	for (tmp = copy; (address = strsep(&tmp, ", ")) && (address[0] != '\0'); /**/) {
 		if (php_pinba_parse_server(address, &new_node, &new_service) != SUCCESS) {
 			free(copy);
 			return FAILURE;

tests/ini_set.phpt

@@ -0,0 +1,37 @@
+--TEST--
+Check for ini_set("pinba.server", ...)
+--SKIPIF--
+<?php if (!extension_loaded("pinba")) print "skip"; ?>
+--FILE--
+<?php
+echo "pinba extension is available\n";
+var_export(ini_get("pinba.server"));
+echo "\n\n";
+
+var_export(ini_set("pinba.server", "one.server"));
+echo "\n";
+var_export(ini_get("pinba.server"));
+echo "\n\n";
+
+var_export(ini_set("pinba.server", "one.server,two.server"));
+echo "\n";
+var_export(ini_get("pinba.server"));
+echo "\n\n";
+
+var_export(ini_set("pinba.server", ""));
+echo "\n";
+var_export(ini_get("pinba.server"));
+echo "\n";
+?>
+--EXPECT--
+pinba extension is available
+''
+
+''
+'one.server'
+
+'one.server'
+'one.server,two.server'
+
+'one.server,two.server'
+''