ftp: never set data->set.ftp_append outside setopt

Since the set value then risks getting used like that when the easy
handle is reused by the application.

Also: renamed the struct field from 'ftp_append' to 'remote_append'
since it is also used for SSH protocols.

Closes #6579

lib/ftp.c

@@ -1578,6 +1578,7 @@ static CURLcode ftp_state_ul_setup(struct Curl_easy *data,
   struct connectdata *conn = data->conn;
   struct FTP *ftp = data->req.p.ftp;
   struct ftp_conn *ftpc = &conn->proto.ftpc;
+  bool append = data->set.remote_append;
 
   if((data->state.resume_from && !sizechecked) ||
      ((data->state.resume_from > 0) && sizechecked)) {
@@ -1604,7 +1605,7 @@ static CURLcode ftp_state_ul_setup(struct Curl_easy *data,
     }
 
     /* enable append */
-    data->set.ftp_append = TRUE;
+    append = TRUE;
 
     /* Let's read off the proper amount of bytes from the input. */
     if(conn->seek_func) {
@@ -1661,8 +1662,7 @@ static CURLcode ftp_state_ul_setup(struct Curl_easy *data,
     /* we've passed, proceed as normal */
   } /* resume_from */
 
-  result = Curl_pp_sendf(data, &ftpc->pp,
-                         data->set.ftp_append?"APPE %s":"STOR %s",
+  result = Curl_pp_sendf(data, &ftpc->pp, append?"APPE %s":"STOR %s",
                          ftpc->file);
   if(!result)
     state(data, FTP_STOR);

lib/setopt.c

@@ -1165,7 +1165,7 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option, va_list param)
      * We want to upload and append to an existing file. Used for FTP and
      * SFTP.
      */
-    data->set.ftp_append = (0 != va_arg(param, long)) ? TRUE : FALSE;
+    data->set.remote_append = (0 != va_arg(param, long)) ? TRUE : FALSE;
     break;
 
 #ifndef CURL_DISABLE_FTP

lib/urldata.h

@@ -1792,7 +1792,7 @@ struct UserDefined {
   BIT(get_filetime);     /* get the time and get of the remote file */
   BIT(tunnel_thru_httpproxy); /* use CONNECT through a HTTP proxy */
   BIT(prefer_ascii);     /* ASCII rather than binary */
-  BIT(ftp_append);       /* append, not overwrite, on upload */
+  BIT(remote_append);    /* append, not overwrite, on upload */
   BIT(ftp_list_only);    /* switch FTP command for listing directories */
 #ifndef CURL_DISABLE_FTP
   BIT(ftp_use_port);     /* use the FTP PORT command */

lib/vssh/libssh.c

@@ -1224,7 +1224,7 @@ static CURLcode myssh_statemach_act(struct Curl_easy *data, bool *block)
         }
       }
 
-      if(data->set.ftp_append)
+      if(data->set.remote_append)
         /* Try to open for append, but create if nonexisting */
         flags = O_WRONLY|O_CREAT|O_APPEND;
       else if(data->state.resume_from > 0)

lib/vssh/libssh2.c

@@ -1880,7 +1880,7 @@ static CURLcode ssh_statemach_act(struct Curl_easy *data, bool *block)
         }
       }
 
-      if(data->set.ftp_append)
+      if(data->set.remote_append)
         /* Try to open for append, but create if nonexisting */
         flags = LIBSSH2_FXF_WRITE|LIBSSH2_FXF_CREAT|LIBSSH2_FXF_APPEND;
       else if(data->state.resume_from > 0)

lib/vssh/wolfssh.c

@@ -585,7 +585,7 @@ static CURLcode wssh_statemach_act(struct Curl_easy *data, bool *block)
         }
       }
 
-      if(data->set.ftp_append)
+      if(data->set.remote_append)
         /* Try to open for append, but create if nonexisting */
         flags = WOLFSSH_FXF_WRITE|WOLFSSH_FXF_CREAT|WOLFSSH_FXF_APPEND;
       else if(data->state.resume_from > 0)