Avoid impossible unionall normalization (#42003)

If the unionall bounds are inconsistent with the wrapper's bound, avoid
throwing due to an impossible type instantiation.

(cherry picked from commit b5b0684)

src/jltypes.c

@@ -1326,8 +1326,15 @@ jl_value_t *normalize_unionalls(jl_value_t *t)
             u = (jl_unionall_t*)t;
         }
 
-        if (u->var->lb == u->var->ub || may_substitute_ub(body, u->var))
-            t = jl_instantiate_unionall(u, u->var->ub);
+        if (u->var->lb == u->var->ub || may_substitute_ub(body, u->var)) {
+            JL_TRY {
+                t = jl_instantiate_unionall(u, u->var->ub);
+            }
+            JL_CATCH {
+                // just skip normalization
+                // (may happen for bounds inconsistent with the wrapper's bounds)
+            }
+        }
     }
     JL_GC_POP();
     return t;

test/core.jl

@@ -7584,3 +7584,6 @@ let S = Tuple{Tuple{Tuple{K, UInt128} where K<:Tuple{Int64}, Int64}},
     @test pointer_from_objref(T) === pointer_from_objref(S)
     @test isbitstype(T)
 end
+
+# avoid impossible normalization (don't try to form Tuple{Complex{String}} here)
+@test Tuple{Complex{T} where String<:T<:String} == Tuple{Complex{T} where String<:T<:String}