BUG/MEDIUM: auth: fix segfault with http-auth and a configuration with an unknown encryption algorithm

Grégoire Morpain reported a segfault when a secured password is used for http
authentication. It was caused by the use of an unsupported encryption algorithm
with libcrypto. In this case, crypt() returns a NULL pointer.

The fix should be backported to 1.4 and 1.5.
(cherry picked from commit c82279c5fc70a6d12ab6efd61e6c9f536e5d4a3f)
diff --git a/src/auth.c b/src/auth.c
index 1069c5b..42c0808 100644
--- a/src/auth.c
+++ b/src/auth.c
@@ -252,7 +252,7 @@
 	fprintf(stderr, ", crypt=%s\n", ep);
 #endif
 
-	if (!strcmp(ep, u->pass))
+	if (ep && strcmp(ep, u->pass) == 0)
 		return 1;
 	else
 		return 0;