[base] Return error if requested driver is not found.

In `open_face_from_buffer` it is possible that a driver is requested but
FreeType was built without the requested module.  Return an error in this
case to indicate that the request could not be satisfied, rather than trying
all existing driver modules.

* src/base/ftobjs.c (open_face_from_buffer): Return `FT_Err_Missing_Module`
if a driver is specified but not found.

src/base/ftobjs.c

@@ -1731,29 +1731,36 @@
   {
     FT_Open_Args  args;
     FT_Error      error;
-    FT_Stream     stream = NULL;
     FT_Memory     memory = library->memory;
 
 
+    args.flags = 0;
+
+    if ( driver_name )
+    {
+      args.driver = FT_Get_Module( library, driver_name );
+      if ( !args.driver )
+      {
+        FT_FREE( base );
+        return FT_THROW( Missing_Module );
+      }
+
+      args.flags = args.flags | FT_OPEN_DRIVER;
+    }
+
     /* `memory_stream_close` also frees the stream object. */
     error = new_memory_stream( library,
                                base,
                                size,
                                memory_stream_close,
-                               &stream );
+                               &args.stream );
     if ( error )
     {
       FT_FREE( base );
       return error;
     }
 
-    args.flags  = FT_OPEN_STREAM;
-    args.stream = stream;
-    if ( driver_name )
-    {
-      args.flags  = args.flags | FT_OPEN_DRIVER;
-      args.driver = FT_Get_Module( library, driver_name );
-    }
+    args.flags |= FT_OPEN_STREAM;
 
 #ifdef FT_MACINTOSH
     /* At this point, the face index has served its purpose;  */