Do not hide errors from database connection attempts

Without these errors it's impossible to figure out what went wrong in
the SSL negotiation. All you get is error 2002 without any means to
diagnose and all important information is issued as PHP warnings.

Issue #12146

Signed-off-by: Michal Čihař <michal@cihar.com>

libraries/dbi/DBIMysqli.php

@@ -84,7 +84,7 @@ class DBIMysqli implements DBIExtension
         }
 
         if ($client_flags === null) {
-            return @mysqli_real_connect(
+            return mysqli_real_connect(
                 $link,
                 $host,
                 $user,
@@ -94,7 +94,7 @@ class DBIMysqli implements DBIExtension
                 $server_socket
             );
         } else {
-            return @mysqli_real_connect(
+            return mysqli_real_connect(
                 $link,
                 $host,
                 $user,