MqWebView: Make save file extension non-const in static funcs

Fixes:

      CC       src/marquee-web-view.o
    src/web-view.c: In function ‘save_type_changed_cb’:
    src/web-view.c:1010:12: warning: assignment discards ‘const’ qualifier from pointer target type
      extension = get_extension(name);
                ^
    src/web-view.c: In function ‘save_response_cb’:
    src/web-view.c:1060:14: warning: assignment discards ‘const’ qualifier from pointer target type
        extension = get_extension(filename);
                  ^

The "extension" variable of save_type_changed_cb() can't be made const
because the string to which it points is modified:

      CC       src/marquee-web-view.o
    src/web-view.c: In function ‘save_type_changed_cb’:
    src/web-view.c:1016:17: error: assignment of read-only location ‘*extension’
        extension[0] = '\0';  /* Remove extension. */
                     ^
    src/web-view.c:1024:17: error: assignment of read-only location ‘*extension’
        extension[0] = '\0';  /* Remove extension. */
                     ^

0 files changed, 0 insertions, 0 deletions