patch 8.2.3970: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/gui_w32.c b/src/gui_w32.c
index d5ffd16..604114c 100644
--- a/src/gui_w32.c
+++ b/src/gui_w32.c
@@ -8393,7 +8393,7 @@
     {
 	if (sign.hImage)
 	    close_signicon_image(&sign);
-	emsg(_(e_signdata));
+	emsg(_(e_couldnt_read_in_sign_data));
     }
     return (void *)psign;