fixed crash in stanza_create_form when text is NULL

xmpp_stanza_get_text may return NULL.
Also fixed memory leak: xmpp_stanza_get_text returns new allocated
string and it must be freed by xmpp_free().

src/xmpp/connection.h

@@ -25,6 +25,8 @@
 
 #include <strophe.h>
 
+#include "resource.h"
+
 xmpp_conn_t *connection_get_conn(void);
 xmpp_ctx_t *connection_get_ctx(void);
 int connection_error_handler(xmpp_conn_t * const conn,