patch 8.2.3830: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/misc2.c b/src/misc2.c
index 9407087..4400d4a 100644
--- a/src/misc2.c
+++ b/src/misc2.c
@@ -1780,7 +1780,7 @@
 
     if (*p_sh == NUL)
     {
-	emsg(_(e_shellempty));
+	emsg(_(e_shell_option_is_empty));
 	retval = -1;
     }
     else