Fix possible memory leak in <MD>_ext()
diff --git a/library/md4.c b/library/md4.c
index da4df7b..1121fd1 100644
--- a/library/md4.c
+++ b/library/md4.c
@@ -333,17 +333,18 @@
     mbedtls_md4_init( &ctx );
 
     if( ( ret = mbedtls_md4_starts_ext( &ctx ) ) != 0 )
-        return( ret );
+        goto exit;
 
     if( ( ret = mbedtls_md4_update_ext( &ctx, input, ilen ) ) != 0 )
-        return( ret );
+        goto exit;
 
     if( ( ret = mbedtls_md4_finish_ext( &ctx, output ) ) != 0 )
-        return( ret );
+        goto exit;
 
+exit:
     mbedtls_md4_free( &ctx );
 
-    return( 0 );
+    return( ret );
 }
 
 #if defined(MBEDTLS_SELF_TEST)