Assert that the back-end has provided a background colour

If we're going to refer to a specific colour, it seems appropriate to
insist that it exists.

1 files changed, 1 insertions, 0 deletions

diff --git a/midend.c b/midend.c
index b89de50..a6f5e6b 100644
--- a/midend.c
+++ b/midend.c
@@ -1312,6 +1312,7 @@ float *midend_colours(midend *me, int *ncolours)
     float *ret;
 
     ret = me->ourgame->colours(me->frontend, ncolours);
+    assert(*ncolours >= 1);
 
     {
         int i;