Fix #8917.

FamInstEnv.normaliseTcApp should normalise arguments even when
the top-level tycon isn't a type family. This was a regression
from 7.6 -- not sure when it happened, but it was probably my
fault. Fixed now, in any case.

compiler/types/FamInstEnv.lhs

@@ -959,9 +959,9 @@ normaliseTcApp env role tc tys
 
   | otherwise   -- No unique matching family instance exists;
                 -- we do not do anything
-  = (Refl role ty, ty)
-  where
-    ty = mkTyConApp tc tys
+  = let (co, ntys) = normaliseTcArgs env role tc tys in
+    (co, mkTyConApp tc ntys)
+    
 
 ---------------
 normaliseTcArgs :: FamInstEnvs            -- environment with family instances