bug #44717: avrdude creates empty flash dump

When about to write an empty flash dump file, warn about this to avoid
surprises.

Document the truncation of trailing 0xFF bytes for flash memory areas.



git-svn-id: svn://svn.savannah.nongnu.org/avrdude/trunk/avrdude@1355 81a1dc3b-b13d-400b-aceb-764788c761c2

update.c

@@ -243,6 +243,9 @@ int do_op(PROGRAMMER * pgm, struct avrpart * p, UPDATE * upd, enum updateflags f
     size = rc;
 
     if (quell_progress < 2) {
+      if (rc == 0)
+        avrdude_message(MSG_INFO, "%s: Flash is empty, resulting file has no contents.\n",
+                        progname);
       avrdude_message(MSG_INFO, "%s: writing output file \"%s\"\n",
                       progname,
                       strcmp(upd->filename, "-")==0 ? "<stdout>" : upd->filename);