fix(view): set modifiable flag for view buffer (#506)

This change provides a fix to somewhat niche use case when user has
`nomodifiable` option enabled globally. Currently, if `nomodifiable`
option is enabled globally it causes plugin to reach unrecoverable state
when 'view' window shows nothing and each key press produces only more
Lua exceptions.

Enabling `modifiable` flag on buffer creation ensures the proper state
of new scratch buffer, no matter what the current global value is.

Co-authored-by: mivort <5783792+mivort@users.noreply.github.com>

lua/which-key/view.lua

@@ -79,6 +79,7 @@ function M.show()
   vim.api.nvim_buf_set_option(M.buf, "filetype", "WhichKey")
   vim.api.nvim_buf_set_option(M.buf, "buftype", "nofile")
   vim.api.nvim_buf_set_option(M.buf, "bufhidden", "wipe")
+  vim.api.nvim_buf_set_option(M.buf, "modifiable", true)
 
   local winhl = "NormalFloat:WhichKeyFloat"
   if vim.fn.hlexists("FloatBorder") == 1 then