ddc_get_dref_by_busno_dor_connector(): fix test for non-removed displ…

…ays <= 1

also just abort in the very very very rare case where more than
one non-removed displays are found and parm ignore_invalid is set.
It's unclear what the proper recovery is in this case, and at present
there are no calls to ddc_get_dref_by_busno_or_connector() with
ignore_invalid set true.

Consider eliminating parm ignore_invalid.

src/ddc/ddc_displays.c

@@ -967,7 +967,11 @@ Display_Ref * ddc_get_dref_by_busno_or_connector(
       }
    }
    // assert(non_removed_ct <= 1);
-   if (non_removed_ct > 0) {
+   if (non_removed_ct > 1) {
+      if (!ignore_invalid) {
+         // don't try to recover from this very very very rare case
+         assert(non_removed_ct <= 1);
+      }
       SEVEREMSG("Multiple non-removed displays on device %s detected. "
                 "All but the most recent are being marked DDC_REMOVED",
                 dpath_repr_t(&result->io_path));