vi: Ensure that the edit buffer ends in a newline

Currently vi assumes that the edit buffer ends in a newline. This may
not be the case. For example:

  $ printf test > test
  $ vi test
  <press 'o'>

We fix this by inserting a newline to the end during initialization.

Signed-off-by: Petja Patjas <pp01415943@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

editors/vi.c

@@ -2315,9 +2315,10 @@ static int init_text_buffer(char *fn)
 
 	update_filename(fn);
 	rc = file_insert(fn, text, 1);
-	if (rc < 0) {
-		// file doesnt exist. Start empty buf with dummy line
-		char_insert(text, '\n', NO_UNDO);
+	if (rc <= 0 || *(end - 1) != '\n') {
+		// file doesn't exist or doesn't end in a newline.
+		// insert a newline to the end
+		char_insert(end, '\n', NO_UNDO);
 	}
 
 	flush_undo_data();