Check for pdflatex tool.

If not present, exit.

contrib/pdf_slideshow.lua

@@ -39,6 +39,7 @@ format (all fields can be the empty string):
 
 ]]
 local dt = require "darktable"
+local df = require "lib/dtutils.file"
 require "official/yield"
 
 local gettext = dt.gettext
@@ -50,6 +51,11 @@ local function _(msgid)
     return gettext.dgettext("pdf_slideshow", msgid)
 end
 
+if not df.check_if_bin_exists("pdflatex") then
+   dt.print_error(_("pdflatex not found"))
+   return
+end
+
 dt.configuration.check_version(...,{4,0,0},{5,0,0})
 
 dt.preferences.register