Avoid conflicts with libinstpatch's default SF2 modulators

By default, libinstpatch silently adds all SF2 default modulators to the
converted DLS voices. Since fluidsynth respects the modulators provided
by libinstpatch, those modulators would conflict with the default
modulator list managed by fluidsynth. This is only noticeable, if the
user used fluidsynth's API to manipulate default modulators.

src/sfloader/fluid_instpatch.c

@@ -359,6 +359,9 @@ static IpatchSF2VoiceCache *convert_dls_to_sf2_instrument(fluid_instpatch_font_t
         return NULL;
     }
 
+    /* do not use the default modulator list of libinstpatch, we manage our own list of default modulators */
+    ipatch_sf2_voice_cache_set_default_mods(cache, NULL);
+
     ipatch_converter_add_input(conv, G_OBJECT(item));
     ipatch_converter_add_output(conv, G_OBJECT(cache));