Kakoune: Invisible character from YouTube chat copying

[alexherbo2]

Copy this line.  There is a character between [​].

[Screwtapello]

hexdump -C says:

00000000  43 6f 70 79 20 74 68 69  73 20 6c 69 6e 65 2e 20  |Copy this line. |
00000010  20 54 68 65 72 65 20 69  73 20 61 20 63 68 61 72  | There is a char|
00000020  61 63 74 65 72 20 62 65  74 77 65 65 6e 20 5b e2  |acter between [.|
00000030  80 8b 5d 2e 0a                                    |..]..|
00000035

The bytes between [] are E2 80 8B, which is the UTF-8 encoding of U+200B ZERO WIDTH SPACE. The h and l keys in Kakoune navigate by Unicode code-point, but not all code-points are visible on-screen, so sometimes the cursor disappears when a zero-width string is selected. Unicode combining characters (which are also zero-width) have the same effect: try pasting Z̭̯̹͈͢a̜̰͇̘̿̎͋ͥḽ̝̺̳̩̩̗g͎̺̩̞o̧ ̤̭̀ͬͧͅt͚̯͉̃̇̇ĕ̟͇͑xt into Kakoune and see what happens.

[lenormf]

Related #1447