Add error checking to mssql_clr_payload

Additional error checking had been added to exploits/windows/mssql/mssql_clr_payload
If an error is encountered when changing the trustworthy or clr setting, the exploit fails with a message.

Author: james

modules/exploits/windows/mssql/mssql_clr_payload.rb

@@ -96,7 +96,10 @@ def get_exploit_version(sql_version_string)
   end
 
   def set_trustworthy(on)
-      mssql_query("ALTER DATABASE [#{datastore['DATABASE']}] SET TRUSTWORTHY #{on ? 'ON' : 'OFF'}", false)
+    result = mssql_query("ALTER DATABASE [#{datastore['DATABASE']}] SET TRUSTWORTHY #{on ? 'ON' : 'OFF'}", false)
+    unless result[:errors].empty?
+      fail_with(Failure::Unknown, "Failed to change Trustworthy setting")
+    end
   end
 
   def is_trustworthy
@@ -112,7 +115,10 @@ def enable_clr(enable)
 EXEC sp_configure 'clr enabled', #{enable ? 1 : 0};
 RECONFIGURE;
     ^
-    mssql_query(query, false)
+    result = mssql_query(query, false)
+    unless result[:errors].empty?
+      fail_with(Failure::Unknown, "Failed to change CLR setting")
+    end
   end
 
   def is_clr_enabled