Check for empty depot path string

Closes #24.

Emacs always passes a depot path to the julia script, but when it's an empty string that
indicates that the depot path elisp variable is not set. This will allow users to set their
own JULIA_DEPOT_PATH without having to configure eglot-jl.

eglot-jl.jl

@@ -33,7 +33,7 @@ src_path = length(ARGS) >= 1 ? ARGS[1] : pwd()
 # - environment:    ENV["JULIA_DEPOT_PATH"]
 # - command-line:   ARGS[2]
 depot_path = get(ENV, "JULIA_DEPOT_PATH", "")
-if length(ARGS) >= 2
+if length(ARGS) >= 2 && ARGS[2] != ""
     depot_path = ARGS[2]
 end