Fixed bug #73418 Integer Overflow in "_php_imap_mail" leads to crash

(cherry picked from commit 99b242a)

Author: weltling

ext/imap/php_imap.c

@@ -3934,7 +3934,7 @@ int _php_imap_mail(char *to, char *subject, char *message, char *headers, char *
 	char *tsm_errmsg = NULL;
 	ADDRESS *addr;
 	char *bufferTo = NULL, *bufferCc = NULL, *bufferBcc = NULL, *bufferHeader = NULL;
-	int offset, bufferLen = 0;
+	size_t offset, bufferLen = 0;
 	size_t bt_len;
 
 	if (headers) {