Core: crypt_r() error handling fixed. The crypt_r() function returns NULL on errors, check it explicitly instead of assuming errno will remain 0 if there are no errors (per POSIX, the setting of errno after a successful call to a function is unspecified unless the description of that function specifies that errno shall not be modified). Additionally, dropped unneeded ngx_set_errno(0) and fixed error handling of memory allocation after normal crypt(), which was inapropriate and resulted in null pointer dereference on allocation failures.