patch 8.1.0563: setting v:errors to a string give confusing error

Problem:    Setting v:errors to a string give confusing error. (Christian
            Brabandt)
Solution:   Change internal error into normal error message.
diff --git a/src/eval.c b/src/eval.c
index 7dfb981..1dae2bf 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -7568,7 +7568,7 @@
 		return;
 	    }
 	    else if (v->di_tv.v_type != tv->v_type)
-		internal_error("set_var()");
+		EMSG2(_("E963: setting %s to value with wrong type"), name);
 	}
 
 	clear_tv(&v->di_tv);