in safe_tempfile(), open a newly created temporary file in "r+b" mode

instead of "w+b" mode, since the latter truncates the file if it already
exists, and we don't need to do that since it's an error if the file
already exists


git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@2593 35c25a1d-7b9e-4130-9fde-d3aeb78583b8

src/files.c

@@ -1134,7 +1134,7 @@ char *check_writable_directory(const char *path)
 
 /* This function calls mkstemp(($TMPDIR|P_tmpdir|/tmp/)"nano.XXXXXX").
  * On success, it returns the malloc()ed filename and corresponding FILE
- * stream, opened in "w+b" mode.  On error, it returns NULL for the
+ * stream, opened in "r+b" mode.  On error, it returns NULL for the
  * filename and leaves the FILE stream unchanged. */
 char *safe_tempfile(FILE **f)
 {
@@ -1165,7 +1165,7 @@ char *safe_tempfile(FILE **f)
     filedesc = mkstemp(full_tempdir);
 
     if (filedesc != -1)
-	*f = fdopen(filedesc, "w+b");
+	*f = fdopen(filedesc, "r+b");
     else {
 	free(full_tempdir);
 	full_tempdir = NULL;