$ characters in passwords are expanded as shell variables

Hi, there. When using a database connection URL with a password containing $ followed by alphanumeric characters (e.g., $0, $test, $admin), vim-dadbod expands these as shell/environment variables, corrupting the password and causing connection failures. Example - Connection URL: ``` postgresql://myuser:SecureP%24ss%240rd@localhost:5432/mydb ``` - Expected decoded password: ``` SecureP$ss$0rd ``` - Actual decoded password (corrupted): ``` SecureP$ss/bin/bashrd ``` Note that `$0` was expanded to `/bin/bash`. Error Message ``` psql: error: invalid integer value "SecureP$ss" for connection option "port" ``` The password corruption in this case causes `psql` to misparse the connection URL. The problem seems to be in `autoload/db.vim`, the `s:expand_all()` function is called unconditionally on all URLs: https://github.com/tpope/vim-dadbod/blob/e95afed23712f969f83b4857a24cf9d59114c2e6/autoload/db.vim#L68 I'm guessing this is to support what it says in the manual of the plugin: ``` Additionally, one can give: * A Vim variable (e.g., g:foo, w:bar, t:baz, b:quux) or environment variable (e.g., $DATABASE_URL) containing a URL. ``` So maybe it can be more selective about what should be expanded? For now, I modified my local installation to avoid that expansion because I don't use it. That fixed my issue and I was able to connect to my postgresql database. Cheers.