Bug 613056 - fix coverify Defect Type: Null pointer dereferences issues 11892 - 11939

https://bugzilla.redhat.com/show_bug.cgi?id=613056
Resolves: bug 613056
Bug description: Fix coverify Defect Type: Null pointer dereferences issues 11892 - 11939
description: Catch possible NULL pointer in vlvSearch_removefromlist().

ldap/servers/slapd/back-ldbm/vlv_srch.c

@@ -458,7 +458,7 @@ vlvSearch_removefromlist(struct vlvSearch** pplist, const Slapi_DN *dn)
             } 
             else
             {
-                prev->vlv_next= curr->vlv_next;
+                if (prev) prev->vlv_next= curr->vlv_next;
             }
             done= 1;
         }