Mobile: No way to open the keyboard for very long prompts on very small screens

[dfabulich]

https://iplayif.com/?story=http%3A%2F%2Fwww.ifarchive.org%2Fif-archive%2Fgames%2Fzcode%2FBronze.zblorb

On an iPod Touch 7th Generation simulator, the <input> line is a teeny tiny 1px-wide sliver on the right edge of the screen. Even with my PR #51, the <input> is nearly impossible to tap on, as the "Tap here to type" hint disappears off the right edge of the screen.

[vmiliantsei]

Possible fix: https://github.com/erkyrath/glkote/pull/71. Inspired by https://github.com/garglk/garglk/blob/bde657b41e67f56e9f2bf58f48eef56ac002030f/garglk/wintext.cpp#L1102.

[erkyrath]

Should be fixed now.