Move `has_eval_provider()` check to `eval_call_provider()` to make sure that
every code path calls it first.

Previously we would, when pynvim was missing, get a nice error message for
`:python3 1`, but not for `:py3file blah`.

Fixes https://github.com/neovim/neovim/issues/9485

Apparently Konsole's terminfo is still broken.

ref #9364
closes #9420

vim-patch:8.0.0428: git and hg see new files after running tests
vim-patch:8.0.0429: options test does not always test everything
vim-patch:8.0.0430: options test fails or hangs on MS-Windows
vim-patch:8.0.0436: running the options test sometimes resizes the terminal
vim-patch:8.0.0488: running tests leaves an "xxx" file behind
vim-patch:8.0.0585: test_options fails when run in the GUI

vim-patch:8.1.0558: some MS-Windows instructions are outdated
vim-patch:8.1.0565: asan complains about reading before allocated block
vim-patch:8.1.0566: SGR not enabled for mintty because $TERM is "xterm"
vim-patch:8.1.0567: error for NUL byte in ScreenLines goes unnoticed
vim-patch:8.1.0568: error message for NUL byte in ScreenLines breaks Travis CI
vim-patch:8.1.0577: tabpage right-click menu never shows "Close tab"
vim-patch:8.1.0578: cannot disable arabic, rightleft and farsi in configure
vim-patch:8.1.0587: GvimExt: realloc() failing is not handled properly
vim-patch:8.1.0589: compilation error in gvimext.cpp
vim-patch:8.1.0592: the libvterm tests are not run as part of Vim tests
vim-patch:8.1.0593: illegal memory access in libvterm test
vim-patch:8.1.0594: libvterm tests fail to run on Mac
vim-patch:8.1.0595: libvterm tests are not run with coverage
vim-patch:8.1.0597: cannot run test_libvterm from the top directory
vim-patch:8.1.0598: indent tests may use the wrong Vim binary
vim-patch:8.1.0605: running make in the top directory echoes a comment 
vim-patch:8.1.0606: 'cryptmethod' defaults to a very old method
vim-patch:8.1.0607: proto files are not in sync with the source code
vim-patch:8.1.0608: coverals is not updating
vim-patch:8.1.0609: MS-Windows: unused variable, depending on the Ruby version
vim-patch:8.1.0610: MS-Windows ctags file list differs from Unix
vim-patch:8.1.0616: NSIS installer is outdated
vim-patch:8.1.0617: NSIS installer gets two files from the wrong directory
vim-patch:8.1.0620: overuling CONF_ARGS from the environment no longer works
vim-patch:8.1.0624: overuling CONF_ARGS from the environment still does not work
vim-patch:8.1.0628: Compiler warning on MS-Windows.
vim-patch:8.1.0635: Coverity complains about null pointer use
vim-patch:8.1.0637: nsis file no longer used
vim-patch:8.1.0646: cannot build with Ruby 2.6.0

- CMake features

We already set back_color_erase in our builtin terminfo
(terminfo_defs.h:conemu_terminfo), so we don't need to set it explicitly
in patch_terminfo_bugs().

- Also remove feature-detection of uv_set_vterm_state(): instead, on
  Windows we always require libuv to have that function.

Problem:    Needlessly searching for tilde in string.
Solution:   Only check the first character. (James McCoy, closes vim/vim#3734)
https://github.com/vim/vim/commit/ef0a1d5ed3566b91143d30ae9de3240f47c6e282