rcfile: let a 'set fill' reenable hardwrapping

Otherwise the user can override a 'set nowrap' in /etc/nanorc only
via the command line.

This fixes https://savannah.gnu.org/bugs/?49593 reported by Shirish.

src/rcfile.c

@@ -1143,8 +1143,10 @@ void parse_rcfile(FILE *rcstream
 		rcfile_error(N_("Requested fill size \"%s\" is invalid"),
 				option);
 		wrap_at = -CHARS_FROM_EOL;
-	    } else
+	    } else {
+		UNSET(NO_WRAP);
 		free(option);
+	    }
 	} else
 #endif
 #ifndef NANO_TINY