progress-bar: hide expected if expected is 0 (unknown)

Sometimes, "expected" can be "0", but in fact means "unknown".

This is for example the case when downloading a file while the http
server doesn't send the `Content-Length` header, like when running `nix
build` pointing to a nixpkgs checkout streamed from GitHub:

⇒  nix build -f https://github.com/NixOS/nixpkgs/archive/master.tar.gz hello
[1.8/0.0 MiB DL] downloading 'https://github.com/NixOS/nixpkgs/archive/master.tar.gz'

In that case, don't show that weird progress bar, but only the (slowly
increasing) downloaded size ("done").

⇒  nix build -f https://github.com/NixOS/nixpkgs/archive/master.tar.gz hello
[1.8 MiB DL] downloading 'https://github.com/NixOS/nixpkgs/archive/master.tar.gz'

This commit also updates fmt calls with three numbers (when something is
currently 'running' too) - I'm not sure if this can be provoked, but
showing "0" as expected doesn't make any sense, as we're obviously doing
more than nothing.

1 files changed, 11 insertions, 4 deletions

diff --git a/src/nix/progress-bar.cc b/src/nix/progress-bar.cc
index 40b905ba3243..8da72bc9481c 100644
--- a/src/nix/progress-bar.cc
+++ b/src/nix/progress-bar.cc
@@ -333,11 +333,18 @@ public:
 
             if (running || done || expected || failed) {
                 if (running)
-                    s = fmt(ANSI_BLUE + numberFmt + ANSI_NORMAL "/" ANSI_GREEN + numberFmt + ANSI_NORMAL "/" + numberFmt,
-                        running / unit, done / unit, expected / unit);
+                    if (expected != 0)
+                        s = fmt(ANSI_BLUE + numberFmt + ANSI_NORMAL "/" ANSI_GREEN + numberFmt + ANSI_NORMAL "/" + numberFmt,
+                            running / unit, done / unit, expected / unit);
+                    else
+                        s = fmt(ANSI_BLUE + numberFmt + ANSI_NORMAL "/" ANSI_GREEN + numberFmt + ANSI_NORMAL,
+                            running / unit, done / unit);
                 else if (expected != done)
-                    s = fmt(ANSI_GREEN + numberFmt + ANSI_NORMAL "/" + numberFmt,
-                        done / unit, expected / unit);
+                    if (expected != 0)
+                        s = fmt(ANSI_GREEN + numberFmt + ANSI_NORMAL "/" + numberFmt,
+                            done / unit, expected / unit);
+                    else
+                        s = fmt(ANSI_GREEN + numberFmt + ANSI_NORMAL, done / unit);
                 else
                     s = fmt(done ? ANSI_GREEN + numberFmt + ANSI_NORMAL : numberFmt, done / unit);
                 s = fmt(itemFmt, s);